unsound - you or someone on this forum may have the reference where Jim suggested that arrangement. What I do remember is that his response was a reaction, not a serious suggestion.
I have tried that setup for on-site recording playback monitors with both the CS5i and CS7.2. Large rooms, placement problems, need for large sweet-spot, plenty of big amplification on site. I put a pair of CS2.2s behind the main out-facing speakers. Speakers were tight back to back, duct-taped to avoid buzzing. BiPolar (same polarity) won.
I liked the more powerful, room-filling deep bass with reduced eigenmodes. There was also an increase in overall sense of spaciousness. But the 'sound' was less true to our remembered live-sound sources (in the same space, in the same session) as well as our headphone reference. In special circumstances it may have some appeal; but it requires deep pockets to implement. I would not recommend it for normal folks with pockets of typical Thiel users.