I'm still interested in trying to understand anything. And since you opened the thread I assume you're interested in talking about it.
I'm glad you have recording experience, this should make the conversation easier. Let's try reducing the problem and try to squeeze out a clearer picture so we're not beating around the bush.
Your hypothesis is that there is one and only one adequate listening volume for a given room/set up. But you state this as 'once you find the spot in your volume control, it's done, don't move it ever again, no matter the source or program material'. Or at least you seem to from what I can see.
Allow me to put forward a small exercise. You record a given event. You make two masters from the same recording: one is simply 5db higher gain than the other, otherwise exactly the same. Disregard clipping, headroom, all the things that would tilt you towards an ideal gain in real life. So you have the same program, just with 5dB difference in gain. Your hypothesis is that you still should not move the reproduction gain/volume, the ideal setting will provide you with the best experience for both masters of this same recording?
Sorry for the reductio ad absurdum, but you seem pretty confident in your claims, so here shouldn't be a problem in digging deeper.