Large bass response peaks typically occuring due to room interactions are interpreted by the ear as "fat" or "slow" bass, and the averaging-out effect of multiple displaced low-frequency sources smooths the in-room response significantly. The subjective result is better pitch definition because we can hear the notes in their proper relationship, and we might well interpret that as faster decay.

I have some experience in blending subwoofer systems with dipole speakers, and in that application multiple subs works very well. I can go into some detail about why if you'd like.

Duke