I can't thank you enough for this calculation. It made a massive improvement.
I read that Denon uses the speed of sound as 300 m/sec rather than 343m/sec for calculation reasons, and that's how the multiplier was determined.
It seems the speed of sound at 20° C is 344 m/sec.
SPEED OF SOUND
I've put my distances in a spreadsheet and multiplied them by 300/344 (0.872 if you prefer) and distances marginally reduced.
It doesn't seem much, but my multi-channelled system is even more in harmony. Almost a sweet spot.
I need a recommendation: For accuracy, I measure my distances with a laser. I've been measuring to the middle of the speaker, but I wonder if I should be measuring to the mid-point between the inner and outer edges of the cone.
BTW, I recall millercarbon describing Home Theater as "crap". Perhaps this is the exact problem he was unable to resolve.