I realize you don't care if we believe you, but I don't like misinformation being spread.
2.6 is the difference from temp alone, then there is humidity, and pressure factored in as well.
Read this article:
You haven't posted a single dyno proving 192, only 182... so for now all I can base this on is the 182 dyno.
I can say my car made 210whp with bolt ons, the burden of proof is on me.
I also know my car is phenominally faster than stock now, so I know i've gained, not hurt it. The mods I've done have been proven time and time again to make power on these cars, unless you have some hidden source of info that none of us have.
Loss of back pressure does not hurt power, loss of exhaust velocity does. The biggest exit with the fastest speed through it will increase max power. Back pressure can sometimes aid torque production in the low end and maybe this is what you mean. Back pressure being present due to the most efficient exhaust velocity (the velocity being the important part and back pressure a side effect) is simply a power loss.