You will probably find the Picatinny rail height on your PSA upper is in between a DPMS Low and a DPMS High rail height.

So the OEM PSA FF tube will have the proper matching height.

That said, I have a few Gen II PA10 / 65 PSA uppers that Midwest Industries DPMS Low rail height  on them and haven't had any issues... NOTE, I don't run laser's or such on the FF rail, so that slight difference in rail height means nothing to me.

Also worth mentioning.... PSA PA10 barrel nuts can some times be tighter then you could imagine.  So I would remove the FF tube and see if the barrel nut is going to cooperate.  

My Gen II PA10 / 65's with a OEM PSA FF tube use these barrel nuts... http://www.jlbillet.com/jl-billet-308-barrel-nut/ , and this retaining key... http://www.jlbillet.com/308-stainless-steel-key-seat-w-rail-screws/

I mention the barrel nut, because my heavy handed mentality snapped one before... it was a sad "ting" snapping noise. I have since stock piled spares. You will need a narrow wrench for them.