It is a p90, not a p90a. I measured the head height and it's currently at 4.2315 or 107.5mm but the problem is that I can't find the definitive stock untouched p90 height spec. I've read 4.25 was the stock height, if that's the case it should be well within acceptable boundaries.
Yes the shaved head must be taken into account, but the shims should have made it close to where it should be.