Custom battleback sometimes can cause a problem like this. Don't read the spoiler if you don't like other people story.
Spoiler
Me too, use max resolution in my project, and I've met the same problem like yours, Moreover my battle engine will visualize actor's battler at the bottom of the screen, so if by any chance I change the original position of enemy y coordinate so it can be placed on the ground(in this case bottom of the screen), it will be covered(hidden or what is the word for this?), so it will not visible. But for floating/flying enemy I believe it's not a problem. So I decide to search a battleback that fit for my case.
What Sharm means probably is usually the ground(the battleback1) area should be 1/2 - 3/4 high from bottom screen, but the battleback2 which for the background(piling up battleback1), should start at 1/2 or 3/4 height from bottom screen. So basically the ground area should cover 1/2 or more height from bottom screen.
Sometimes I would like a battler that don't have a shade and use only battleback1(ground area), so they are not that weird .
What I can suggest is changing battleback. Sorry if not helping.
P.S : Oh yeah if that battleback is made from a single battleback, then it's more complicated, you really need to change to another one. I sometimes thinking, that's why there are two battleback(battleback1 and battleback2), so if using two battleback will makes the battler looks weird, the user can try to use only battleback1.
(Damn it, I need to improve my english).