^^^ I agree except the effect is due to the added reflections from the side or back waves, not (or not just) the phasing.
Because of room interaction and listener preferences it will always be somewhat speculative.
Bipolar - radiates in two directions, often "front" and "back" relative to the mounting surface, so if on a side wall you might get a little direct and some reflected with a path length from the "rear-facing" driver to the back wall and back to the listener, and of course some from other reflections from the "front" driver etc.
Dipole = radiates equally from the front and the back, so you'll get some direct sound (if it fcaes you) plus reflected/dispersive sound from the back wave that hits the wall immediately behind and bounce around.
To me, for surrounds, dipoles give a more "diffuse" overall stage with still a goodly amount of direct sound and I like that effect .The only bipoles I have heard, and only a little, were my friend's B&Ws plus some trials in a store demo. To me, the bipoles do not disperse the sound as much so the net effect is more directional sound than reflected. It is easy to hear but hard to describe, at least for me. I find my dipoles to be more "enveloping" if that makes sense. Which is better is up to you, and may even depend upon the source material.
FWIWFM - Don
"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley