So are you running a heavy buffer or extra power spring now? I had issues with an 18" rifle length gassed barrel, but my 16" carbine gas and 18" mid-length gas behave with 90 to 120grn pills with extra strength flat springs, H2 buffers, and M16 BCG's (a touch heavier). My current 6.8 is running 2 turns open from full closed on an adjustable gas block also.
This isn't Bison's first rodeo, I've known enough guys with their kit that runs phenomenally, so I'd be surprised if they'd mess up on something as simple as a gas port diameter. No big deal to open it up anyway. I personally would rather have my port be way too large and have an adjustable block be the gate-keeper than be restricted on what bullet weight I can run.
That said - you'll be just fine running heavier pills anyway.