PSX gas block height

[mikejg]

Does anyone know if the rail on the gas block is the same plane as the rails on the upper?

My buddy recently got the PSX and put a Troy fixed sight on the gas block rail, but we had a hell of a time getting it zeroed. I didn't think about it being on a different plane while we were at the range. Does he need a different height sight for the gas block?

Thanks.

Mike