diff --git a/concat-css.php b/concat-css.php
index 18024d8..f76864e 100644
--- a/concat-css.php
+++ b/concat-css.php
@@ -38,17 +38,18 @@ function __construct( $styles ) {
 	function do_items( $handles = false, $group = false ) {
 		$handles = false === $handles ? $this->queue : (array) $handles;
 		$stylesheets = array();
-		$siteurl = apply_filters( 'page_optimize_site_url', $this->base_url );
+
+		// get the website base url
+		$siteurl = apply_filters( 'page_optimize_site_url', $this->dependency_path_mapping->base_url );
 
 		$this->all_deps( $handles );
 
-		$stylesheet_group_index = 0;
 		// Merge CSS into a single file
-		$concat_group = 'concat';
-		// Concat group on top (first array element gets processed earlier)
-		$stylesheets[ $concat_group ] = array();
+		$style_index = 0;
+		$style_group = array();
 
 		foreach ( $this->to_do as $key => $handle ) {
+
 			$obj = $this->registered[ $handle ];
 			$obj->src = apply_filters( 'style_loader_src', $obj->src, $obj->handle );
 
@@ -63,16 +64,18 @@ function do_items( $handles = false, $group = false ) {
 			$css_url_parsed = parse_url( $obj->src );
 			$extra = $obj->extra;
 
-			// Don't concat by default
-			$do_concat = false;
+			// try to concat static css files
+			$do_concat = true;
+
+			if ( 0 == strpos( $css_url_parsed['path'], '.css' ) ) {
 
-			// Only try to concat static css files
-			if ( false !== strpos( $css_url_parsed['path'], '.css' ) ) {
-				$do_concat = true;
-			} else {
 				if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
 					echo sprintf( "\n<!-- No Concat CSS %s => Maybe Not Static File %s -->\n", esc_html( $handle ), esc_html( $obj->src ) );
 				}
+
+				$style_group['not-static-'. $style_index++ ] = $handle;
+
+				$do_concat = false;
 			}
 
 			// Don't try to concat styles which are loaded conditionally (like IE stuff)
@@ -80,6 +83,8 @@ function do_items( $handles = false, $group = false ) {
 				if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
 					echo sprintf( "\n<!-- No Concat CSS %s => Has Conditional -->\n", esc_html( $handle ) );
 				}
+
+				$style_group['conditional-'. $style_index++ ] = $handle;
 				$do_concat = false;
 			}
 
@@ -88,6 +93,8 @@ function do_items( $handles = false, $group = false ) {
 				if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
 					echo sprintf( "\n<!-- No Concat CSS %s => Is RTL -->\n", esc_html( $handle ) );
 				}
+
+				$style_group['rtl-'. $style_index++ ] = $handle;
 				$do_concat = false;
 			}
 
@@ -97,6 +104,8 @@ function do_items( $handles = false, $group = false ) {
 				if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
 					echo sprintf( "\n<!-- No Concat CSS %s => External URL: %s -->\n", esc_html( $handle ), esc_url( $css_url ) );
 				}
+
+				$style_group['external-'. $style_index++ ] = $handle;
 				$do_concat = false;
 			}
 
@@ -107,6 +116,8 @@ function do_items( $handles = false, $group = false ) {
 					if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
 						echo sprintf( "\n<!-- No Concat CSS %s => Invalid Path %s -->\n", esc_html( $handle ), esc_html( $css_realpath ) );
 					}
+
+					$style_group['invalid-'. $style_index++ ] = $handle;
 					$do_concat = false;
 				}
 			}
@@ -115,10 +126,12 @@ function do_items( $handles = false, $group = false ) {
 			$exclude_list = page_optimize_css_exclude_list();
 			foreach ( $exclude_list as $exclude ) {
 				if ( $do_concat && $handle === $exclude ) {
-					$do_concat = false;
 					if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
 						echo sprintf( "\n<!-- No Concat CSS %s => Excluded option -->\n", esc_html( $handle ) );
 					}
+
+					$style_group['excluded-'. $style_index++ ] = $handle;
+					$do_concat = false;
 				}
 			}
 
@@ -131,31 +144,27 @@ function do_items( $handles = false, $group = false ) {
 			$do_concat = apply_filters( 'css_do_concat', $do_concat, $handle );
 
 			if ( true === $do_concat ) {
+
+				$style_group[ 'concat-' . $style_index ][] = $handle;
+
 				$media = $obj->args;
 				if ( empty( $media ) ) {
 					$media = 'all';
 				}
 
-				$stylesheets[ $concat_group ][ $media ][ $handle ] = $css_url_parsed['path'];
+				$stylesheets[ 'concat-' . $style_index ][ $media ][ $handle ] = $css_url_parsed['path'];
 				$this->done[] = $handle;
 			} else {
-				$stylesheet_group_index ++;
-				$stylesheets[ $stylesheet_group_index ]['noconcat'][] = $handle;
-				$stylesheet_group_index ++;
+				if ( $this->do_item( $handle, $group ) ) {
+					$this->done[] = $handle;
+				}
 			}
 			unset( $this->to_do[ $key ] );
 		}
 
 		foreach ( $stylesheets as $idx => $stylesheets_group ) {
 			foreach ( $stylesheets_group as $media => $css ) {
-				if ( 'noconcat' == $media ) {
-					foreach ( $css as $handle ) {
-						if ( $this->do_item( $handle, $group ) ) {
-							$this->done[] = $handle;
-						}
-					}
-					continue;
-				} elseif ( count( $css ) > 1 ) {
+				if ( !empty( $css ) ) {
 					$fs_paths = array();
 					foreach ( $css as $css_uri_path ) {
 						$fs_paths[] = $this->dependency_path_mapping->uri_path_to_fs_path( $css_uri_path );
@@ -176,7 +185,7 @@ function do_items( $handles = false, $group = false ) {
 						}
 					}
 
-					$href = $siteurl . "/_static/??" . $path_str;
+					$href = $siteurl . $this->dependency_path_mapping->site_subdir_path . "/_static/??" . $path_str;
 				} else {
 					$href = Page_Optimize_Utils::cache_bust_mtime( current( $css ), $siteurl );
 				}
diff --git a/concat-js.php b/concat-js.php
index 46d9020..3d03225 100644
--- a/concat-js.php
+++ b/concat-js.php
@@ -58,7 +58,8 @@ protected function has_inline_content( $handle ) {
 	function do_items( $handles = false, $group = false ) {
 		$handles = false === $handles ? $this->queue : (array) $handles;
 		$javascripts = array();
-		$siteurl = apply_filters( 'page_optimize_site_url', $this->base_url );
+		$siteurl = apply_filters( 'page_optimize_site_url', $this->dependency_path_mapping->base_url );
+
 		$this->all_deps( $handles );
 		$level = 0;
 
@@ -229,7 +230,7 @@ function do_items( $handles = false, $group = false ) {
 						}
 					}
 
-					$href = $siteurl . "/_static/??" . $path_str;
+					$href = $siteurl . $this->dependency_path_mapping->site_subdir_path . "/_static/??" . $path_str;
 				} elseif ( isset( $js_array['paths'] ) && is_array( $js_array['paths'] ) ) {
 					$href = Page_Optimize_Utils::cache_bust_mtime( $js_array['paths'][0], $siteurl );
 				}
diff --git a/dependency-path-mapping.php b/dependency-path-mapping.php
index 7170edd..48d6d45 100644
--- a/dependency-path-mapping.php
+++ b/dependency-path-mapping.php
@@ -10,6 +10,8 @@ class Page_Optimize_Dependency_Path_Mapping {
 	public $site_url;
 
 	// Save URI path and dir for mapping URIs to filesystem paths
+	public $base_url = null;
+	public $site_subdir_path = null;
 	public $site_uri_path = null;
 	public $site_dir = null;
 	public $content_uri_path = null;
@@ -29,9 +31,15 @@ function __construct(
 		if ( null === $site_url ) {
 			$site_url = is_multisite() ? get_site_url( get_current_blog_id() ) : get_site_url();
 		}
+		// parse the site url for further use
+		$url_parsed = parse_url($site_url);
+
+		$this->base_url = $url_parsed['scheme'].'://'.$url_parsed['host'];
+		$this->site_subdir_path = str_replace( $this->base_url, "", $site_url );
+
 		$site_url = trailingslashit( $site_url );
 		$this->site_url = $site_url;
-		$this->site_uri_path = parse_url( $site_url, PHP_URL_PATH );
+		$this->site_uri_path = $url_parsed['path'];
 		$this->site_dir = trailingslashit( $site_dir );
 
 		// Only resolve content URLs if they are under the site URL
@@ -87,6 +95,11 @@ function uri_path_to_fs_path( $uri_path ) {
 			return false;
 		}
 
+		// Adds the sub-directory path if not present, like all other resources have if the website is hosted into a sub-folder
+		if ( ! empty( $this->site_subdir_path ) && ! page_optimize_starts_with( $this->site_subdir_path, $uri_path ) ) {
+			$uri_path = $this->site_subdir_path . $uri_path;
+		}
+
 		// The plugin URI path may be contained within the content URI path, so we check it before the content URI.
 		// And both the plugin and content URI paths must be contained within the site URI path,
 		// so we check them before checking the site URI.
diff --git a/page-optimize.php b/page-optimize.php
index 4d3ac9b..9732798 100644
--- a/page-optimize.php
+++ b/page-optimize.php
@@ -26,7 +26,7 @@
 // TODO: Copy tests from nginx-http-concat and/or write them
 
 // TODO: Make concat URL dir configurable
-if ( isset( $_SERVER['REQUEST_URI'] ) && '/_static/' === substr( $_SERVER['REQUEST_URI'], 0, 9 ) ) {
+if ( $_SERVER['REQUEST_URI'] != false && stripos( $_SERVER['REQUEST_URI'], '/_static/' ) !== false ) {
 	require_once __DIR__ . '/service.php';
 	exit;
 }
diff --git a/service.php b/service.php
index eea8aa1..99a4615 100644
--- a/service.php
+++ b/service.php
@@ -187,8 +187,13 @@ function page_optimize_build_output() {
 			page_optimize_status_exit( 500 );
 		}
 
+		// Removes source mapping URLs as they are unnecessary after concatenation
+		if ( false !== strpos( $buf, 'sourceMappingURL' ) ) {
+			$buf = preg_replace('/\/[\/*].*sourceMapping.+/', "" , $buf );
+		}
+
 		if ( 'text/css' == $mime_type ) {
-			$dirpath = '/' . ltrim( $subdir_path_prefix . dirname( $uri ), '/' );
+			$dirpath = '/' . ltrim( dirname( $uri ), '/' );
 
 			// url(relative/path/to/file) -> url(/absolute/and/not/relative/path/to/file)
 			$buf = page_optimize_relative_path_replace( $buf, $dirpath );