… SUB distances should not be this HARD.
But they often are
. This is the dreaded room effect. See this
https://en.wikipedia.org/wiki/Loudspeaker#Placement
Placement
In a typical rectangular listening room, the hard, parallel surfaces of the walls, floor and ceiling cause primary
acoustic resonance nodes in each of the three dimensions: left-right, up-down and forward-backward. Furthermore, there are more complex resonance modes involving three, four, five and even all six boundary surfaces combining to create
standing waves.
Low frequencies excite these modes the most, since long wavelengths are not much affected by furniture compositions or placement. The mode spacing is critical, especially in small and medium size rooms like recording studios, home theaters and broadcast studios. The proximity of the loudspeakers to room boundaries affects how strongly the resonances are excited as well as affecting the relative strength at each frequency. The location of the listener is critical, too, as a position near a boundary can have a great effect on the perceived balance of frequencies. This is because standing wave patterns are most easily heard in these locations and at lower frequencies, below the
Schroeder frequency – typically around 200–300 Hz, depending on room size.
It is possible (I'm guessing here) that your receiver came up with the 19+ foot estimate when your second sub was really 12 feet away because the sound reflected off a wall was louder than sound coming directly from the sub. That path, including the wall (ceiling or floor) bounce, was about 19 feet.
If your sub has a polarity switch on it, you might try the YPAO routine with reversed polarity on that sub. It may or may not work differently.
