Weseixas, I'm sorry but my figures correlate very closely with Atmasphere, 96 versus 98 sensitivity, 120 versus 140 good watts, my sound level of 117dB at 1m, his of 110 at 3m. Check out a text book, you lose 6db per doubling of distance -- from 1m to 2m down 6dB, from 2m to 4m (a doubling) down another 6dB, total 12dB. Remember, a 3dB difference is only just detectable by ear.
I also pointed out previously that the 10 to 20 times power is completely unnecessary IF the system is not distorting. I thus agree, that if the system is poorly engineered then you would need a very large "safety" margin, to compensate for the inadequacies of the setup.
Finally, the room size has nothing to do with it. Having personally experienced what is possible with a nominally mediocre setup, which has been tweaked in every which way, in a very nondescript normal room, I say that with total confidence.
Frank