bilpelt, the first time I shot my .308 suppressed in competition, it really changed the handling characteristics of my rifle. It's outstanding shooting off a stable platform, but when I perform standing, kneeling or sitting shots, the rifle's balance is off, which is difficult to compensate for, at least for me. I thought that I could just go out and shoot a competition with out practice and everything would stay the same, it didn't. I still have not perfected it, just that added weight on the end on the barrel made a big difference in balancing the rifle. I need to get in a lot more practice, before I compete again.
I've also noticed some of the guys went from suppessor's to muzzle breaks. However, shooting next to these guys with their blasts can be tough at times, although, I may get a muzzle break in addition to using the suppressor, just to try it.
From all the research that I've done on suppressor's, and I am by no means an expert, your POI shift seems about the norm for a suppressed rifle. I use a Thunderbeast and a Surefire and I am right about where you're at, as far as shift is concerned with both brands.