Stan, think about it like this:
You have a 100hp engine that makes 65hp at the wheels. That's 35% loss, yes?
Then you whack some gas on it and it now makes 150hp at the engine. Would you expect the wheel hp to be 97.5hp (35% loss) or more like 115hp (the same actual hp loss as the original scenario)?
Assuming the same driveline (flywheel/flexplate, clutch/converter, gearbox, tailshaft, diff, driveshafts/axles), why should there be significantly more (nearly 12% extra) drivetrain loss just because you upped the engine hp?
Sure there might be more heat/noise created (in the drivetrain) but sticking to an arbitrary and uniform drivetrain loss percentage or amount is ridiculous. Even so, I've heard some otherwise very switched on people suggest it as fact.