I have personally never believed that transmission loss can be calculated as a percentage.

My RST has always shown around 25-30bhp in transmission losses regardless of progression in power. OK, so it was measured using coast-down, but surely that's fairly accurate.

Also, it seems odd that most 4wd cars lose 80-100bhp, I have even seen 500bhp 4wd cars quote those kinds of losses, but suddenly 600-800bhp 4wd cars magically lose 250-300bhp somewhere. The amount of 600-800bhp cars that only quote 500-600 ATW is untrue.