Hi Dean,
The figures I mentioned in my article are the theoretical decreases in SPL with a doubling of distance, but since Floyd Toole was (is. .) my mentor, I'll certainly yield to his research and the figures quoted in his excellent book.
However, I'd point out that there is a lot of variation in personal preferences of playback levels. Even when I was on the NRC listening panel with Floyd Toole, my colleagues, including Floyd, listened louder than I did. I'd often sit farther back in the room to reduce the SPL at my seat. On average, I'd estimate they preferred playback levels at least 3 dB louder than what I was comfortable with.
In terms of my Axiom colleagues, I joke about some of the playback levels they like, which I find "deafening", at least 6 dB to 10 dB louder than my preferred settings (a 10-dB increase in loudness is subjectively termed "twice as loud"). And the playback levels they like are not uncommon--visitors to the listening room at the factory (of all ages) tend to use higher playback levels.
So factor in your own preferences, as it seems you have.
Regards,
Alan
