picture size of Featured Page Slider doesn't match

I'm using this Featured Page Slider with a page which has a featured image with a resolution of 3872 x 2592. The problem now is that the image isn't cut to the themes optimal size of 1680x720. I have used Regenerate Thumbnails and i can see that this plugin has created a picture with the correct size (Testimage-1-1680x720.jpg). So why isn't Catch Adaptive using this image?