Would you say the 30 watt mode is 4 times louder than the 7 watt mode bro? Is it twice as loud as the 15 watt mode?
Look, I'm not questioning your statement about double power = double db. That is very spot on. Really. It's just that I can perceive a difference in volume between a 15w vs 30w. Clean. That is my personal experience after owning 7, 15, 30, and 100w tube amps.
So, again, ymmv.