When I do 6/24 the subwoofer plays along with the left side speaker. Lost all the punches and sound muddy. Flip the phase to REV and it's much tighter, but the bass seems to play by itself (from the back). The image appears to come from the right side.

Also, I don't know if it's only me. My subwoofers are almost always TA in the 154/155in region no matter what slope I choose.