What about adding another point of contact on the top portion of the mount? Like this...Oh, I could see exactly what was happening. It was a vertical stringing do to
the mount base shifting towards the muzzel. After 10 or so rounds the rear of the base would jack up a little which canted the scope towards the ground making it shoot at least 4 feet high at 50 yards, very bad, I shot over the range berm at least once. I re-torqued everything and tryed it again, this time I stopped at around 7 rounds as I could see it was going to do the same thing again. The windage was spot on untill the mount canted forward.
I bore sighted it at 50 yards and was with in 6 inches of a bullseye with my first shot, it looked very promising to begin with.I went ahead and shot the rifle with the iron sights since this was the first time I had shot it. It had a loose front sight and wouldn't hold zero windage wise, I'm glad I had a couple of other rifles to shoot. Still had a good time with my son and a friend from work.
That might even out the downforce on the mount and provide another contact point that would fight some of the tendency to want to shift forward or backward upon recoil.
BTW, I'm not trying to shoehorn my opinions into your design or anything, I just find these sorts of engineering puzzles to be a lot of fun. Feel free to tell me, "I've got it covered. Piss off".