Hello Myatu,
no, the preview doesn’t show the overlay, only the image.
One, maybe interesting, thing is, that when I set overlay, the preview show repeated image but no overlay. Even if the “Tiling” option is set to “No tiling”. When the overlay is deactivated, preview show correctly only one image (no repeat).
I’ve set up a new WP site without other plugings (behaviour is the same). If this would help you to determine the issue I can send you link and login via mail. Just let me please know.