Tamid,
If you can shoot low gun and hit things and get no cheek slap, then it has to do with your mount when shooting gun up. My guess is that you are rolling your head after the mount. Head rolling does not necessarily change your eye to rib relationship but makes a huge difference in recoil management.
If happens with all guns of different fit, then it is probably not gunfit. I can shoot all sorts of different fitting guns and never get cheek slap but my brother does with any gun.
We will have to go out to the range and I can sort it out after watching you shoot, both gun-up and gun-down.
