Noticed the same trend up top. As I'm sure you are aware, rather than being native the bidirectional pattern (as well as all others) is derived, so there is significantly different stuff going on with respect to the acoustic capsule geometry relationships in comparison to standard single and dual diaphragm fig-8's.
Len, as a TetraMic user (for those following along, that's CoreSound's 1st order, 4 channel ambisonic microphone which proceeded the 2nd order 8ch OctoMic), I'm curious how much the TetraMic bi-directional pattern differs. The TetraMic is capable of a well behaved Blumlein pattern itself. Are the two similar with regards to the behavior of all 1st order patterns? Or is the 2nd order capability able to be used to demonstrably improve upon the 1st order pattern behavior of the TetraMic?
What most interests me about the OctoMic is potential for deriving directional pickup patterns unavailable to 1st order microphones. Specifically cardioid-like patterns with a narrow front lobe similar to that of a 1st order figure-8, yet with minimal back lobe sensitivity (and acceptably minimal side lobe behavior). Can you tell us more about those aspects?
With the TetraMic in typical taper use, I generally found myself gravitating toward dialing in crossed supercardioid to hypercardioid patterns with a somewhat wider included angle rather than Blumlein. That's probably not surprising to folks here intimately familiar with the use of coincident pair techniques in taper situations. It is in that pattern range where I expect the advantage of a higher order system to offer some interesting possibilities and the potential of significant improvement.
BTW, that Stile Antico recording is very nice.