I don't have amphibians nifty stuff so it is hard to tell if if my carrier is bottoming out or not but what I have is similar to "OBC test 6".
In this configuration I have a custom carbon buffer tube/stock that is A5 length, 12.5" barrel, OBC, 556 Tubb, Kynshot RB5007, Griffin Paladin suppressor, .075 gas port (if memory serves) but I also use an adjustable gas block, and a .12" spacer in the buffer tube.
I also have an unusual gas system somewhere between a carbine and mid, I seem to recall it was 11" but I would have to tear the rifle down to measure and I am far too lazy for that.
Much of this setup I derived from info provided by Amphibian when I posted a couple years ago looking for info about the OBC.