The volume scale isn't linear either, it's dB based so not sure how you come up with 85% power. If you're at -11, changing it to -8 uses double the power or lowering it to -14 reduces use by 50%. The goal of the reference volume scale is such that at "0" you're at THX reference levels (85dB average with allowance for 20dB peaks), which is quite loud, but would take 10x the power to go from say -10 to 0.