How to prevent slider concertina action

Hello Bellini team, I don’t really have a link to give you as I only have it in “Live Preview” at the moment to test it out for my site. I have attempted to change the image for one of my own and adjust sizes accordingly. When I go to fullscreen the section slides to a greater height showing whitespace at the top and bottom. I cannot work out how to prevent this. I guess it is a sort of concertina action. I set the max-height to 500 but the section slides out to 561. When I scroll down the page (or open Inspect) it slides back to just the image and the whitespace disappears; I would like it to stay that way if possible.