Multiple Small Subs - Geddes Approach

This topic gets a lot of attention on ASR...how many recordings are mono bass vs stereo bass. Analysis of tracks, including older CD tracks, has been showing more is recorded in stereo than commonly presumed.
Maybe the old practice of needing to mono bass for vinyl, died off earlier and more prevalently than realized?
And when the wavelengths in a room are long enough to sum as one?
Using multiple subs ontop. The advantage of "stereo" bass is what?

Thats how i read his comment at least. Near 100% summation at those frequencies.
 
And when the wavelengths in a room are long enough to sum as one?
Using multiple subs ontop. The advantage of "stereo" bass is what?
How does the length of rooms have anything to do with wavelength summations? Summations, not formations from modes.

I think removing the idea of recordings predominantly are mono bass, is a first step in questioning how bass is heard in rooms.