Went to the range today.
With the "thread relief shim" in place there was very little POI shift.
Went back and forth a few times to verify. It's not perfect repeatability but it's close. POI shift was less than 2 inches every time, and sometimes less.
That amount of shift doesnt bother me. I zero'd with the suppressor and plan to shoot it that way.
Problem solved.... and my groups tightened a little especially with 155 A-Max. This barrel seems to prefer the 155 A-Max so far.
Also shot the SCAR 17s. It seems that POI shift is always 4 or more inches down. I may try some shims to see if I can shift it but... it's a lightweight barrel. I can almost see it sag (LOL!) when the Can is on.