Re hardcore science, well there are books (available on Amazon) on acoustics as they relate to audio systems, but I don't know how much they would help you in setting up your system.
I'm not familiar with the proper set up of bi-directional speakers. Forward firing boxes, panels, and electrostatics yes. I'm really not familiar with omni's or bi-directional boxes either, so I'm not a really good source of information for you.
The 'between the speakers" I referred to was from the inside of your forward facing drivers. I wasn't suggesting anything in particular, just that depending on the strength of the off axis signal that reflections off this wall could affect your systems sound (note I referred to 2d reflection points) but its contribution would be small(er) compared to the rear drivers reflecting off any of the walls sounding your speakers.
But something I can rather confidently suggest you try is bringing your speakers out further into your room. This will give you better separation of the direct sound vs the sound of the rear wall, resulting in a clearer sound. At least 5 ft. Further won't hurt but be mindful of the change in bass response due to room nulls and nodes.
FWIW.