It really doesn't matter whether the bipolar-wired speakers face forward or backward in relation to the fronts (in regards to phase). What matters is that the opposing drivers in the speaker itself are wired in phase with each other for a bipole configuration. If the dipole/bipole speakers have instructions for L or R placement, use them as so. But if they don't, you needn't worry about it. Just experiment with placement as with all things audio.
One thing you can experiment with is reversing the polarity at the input terminas if you think that the two rear speaker systems are at odds with one another and are playing at less-than-ideal. The polarity would be reversed on only one speaker system. My bet is that you wouldn't be able to tell a difference.
I built my DIY dipoles as mirror images, and also made the front side look different than the back. This would be classified as dedicated left/right. It DOES make the most sense to build them that way, but commercial offerings have to keep marketing, inventory and selling in mind.