Have you sweet spotted the reg at two turns in of the IVG?
I have found that if I set my reg at a conservative sweet spot - and then turn in the IVG - I have to re-set the sweet spot of the reg. It can change.
Turn it two turns in - set the reg at that point - and then see where you are. Give it three turns - and see if the reg can be adjusted to give you a little more FPS.