IMHO, It is better to have the surround channel less localizable, even for MCH music, as well as movies. Your focus should be forward, at the screen (movies) or front stage (band), with the surround effects ancillary, an enhancement of what is occurring in front of you. If there is a mix that requires localization, such as an instrument being played behind you, it's pure gimmick. That's why those things failed. The novelty wears of quickly and you realize that no concert or music event you went to had you sitting inside the band, unless you were playing, rather than observing.
Btw, bipoles add spaciousness and some diffusion, but on say a MCH music soundtrack, you can still localize them...if that is your desire.
When you place such a speaker in the corner like you have diagrammed, you get a direct sound from the driver set facing the couch (and a portion of a the 2nd set mixed in), as well as reflections from both sets off walls. With a monopole in the same position, you get the same mix of direct sound and reflections off the wall, it's just that the percentage of reflections is lower than the bipole. Both will be somewhat diffuse/less localizable because of the early reflections, especially behind you, where you don't hear as well as in front of you, but the bipole will be more diffuse and more spacious because of the higher percentage of reflected sound, having a larger area behind you of where the "effect" might be coming from. This tends to work better for movies, less so for MCH music. But who wants to hear a guitar or violin playing clearly behind you? What percentage of attended music events does that recreate for you?