First off, maxing out the HPR is not a good plan. You will actually decrease your FPS if the reg is outputting a normal amount of pressure, because the ram wont be able to open the poppet as well due to all the pressure. I would rebuild both regs, and the rammer, and try again. That is going to be the most likely cause. Then, I would double check the Dwell, and make sure that the LPR screw is flush. And after that, try switching the battery. If none of those work, report back.
I understand the idea of a sweetspot and after that either increasing or decreasing the output pressure will cause a loss in velocity but we tried half turns from the lowest output to the highest output and there was no change in velocity.
I will double check the regulator and do a factory reset on the board, it has been doing this for a long time so it is not low battery.