While I've been using your plugin for a long time and love it, I've recently started placing it in the mu-plugin directory b/c it has become so vital to the sites I'm building. However, I've noticed that when I do this, the url paths the plugin builds are incorrect.
The issue is line 18 of the wpcf.php file.
define( 'WPCF_RELPATH', plugins_url() . '/' . basename( WPCF_ABSPATH ) );
if you changed it to
define( 'WPCF_RELPATH', plugins_url( null, __FILE__ ) );
I think that will correct the issue and still give the expected results regardless of which plugin directory the plugin in placed into.
Thank you for your time and the great plugin.