suppressor use and POI shift

[Klem]

Correct, although I suspect it has less to do with harmonics and more to do with the weight changing the way the gun recoils while the bullet is still in the barrel. Plus you get a few more fps due to freebore boost. While the suppressor is not as efficient as a barrel in containing pressure it does give you up to 10fps more. This, plus the weight on the end of the barrel is what changes your POI.

The few with no difference between shooting on and off is indeed rare - I have never seen it. A difference of about 1Mil/3MOA is normal.