My 6' tall Carver ribbon speakers are natural dipoles. They need 3+ feet from the front wall to avoid early cancellation, but are awesome after that. They image precisely. The back wave is for three dimensional presence in space (i.e. Real sounds tend to be omnidirectional dipoles in nature so that's what your brain is used to hearing in the real world). That's also why most box speakers sound like "stereo" and not real life, IMO. But the need breathing room and face front/back not the null to the side thing made for old style surround use. Regular speakers also have a back wave, but it's normally absorbed internally with the insulation and nowhere for the sound to go inside the box.
Bipoles are man-made creations designed to be in phase rather than out of phase relative to each other. The idea is to get that 3D presence effect without the need to keep the speakers well away from the walls. Again, that is front/back use, not facing the null area of the speaker for surround use.
As surrounds, bipoles image better than dipoles (no dead null effect to the sides), but faced from the sides, they tend to be more nebulous than direct facing monopoles. However, the angled variety on the side walls placed between rows gives essentially an array of two sets of monopoles, one facing each row so each seating area row gets even sound without having to buy two sets of side surrounds.
I use three set of bed level side surrounds in my three row home theater (front wide, side, side #2 and then rears in the back plus regular fronts), but only three sets of overheads front, middle and rear) so I use angled bipoles in the middle in the Auro-3D location so the front and rear rows get even middle coverage (faces both rows that way). I don't hear any imaging issues blending with front/rear heights.
