Compensator ports do not lower the PF. Once the bullet leaves the barrel, it's going as fast as it ever will. The only "ports" that would lower your PF would be popple holes in the barrel that bleed off gas before the bullet exits the barrel.
That said, sometimes variances in PF from one gun to another have more to do with the actual barrel. No two barrels are exactly alike, no matter how tight the manufacturing tolerances. Fire the same load through two identical guns and you probably will not get the same results.
Thanks for reply, I agree that no two guns are alike, and it makes sense about the compensator ports, I was under the impression all the holes would lower the PF. This gun does have popple holes, it has 6. Does wear on the barrel bleed PF over time? I would assume so, but I wouldn't know how much, after how many rounds. I'm not sure how old the gun is, but I think she has seen better days.