Ok lets see if we can wrap this up quickly before Fitz says something even dumber.
Back to what JJ said, in the "Time alignment" thread, he's referring to (inter) driver phase integration
at the source, not inter channel. He was a bit ambiguous with the "surprisingly low", but to my knowledge, 700hz on up and you're good to go, especially with as you noted percussive attacks. I'll have to dig through my library for the AES references, but suffice to say, your XO being 180hzz and the panel running full bandwidth above that is going to automatically take care any multi-driver phase integration issues >700Hz.
Note I'm not saying inter-ch isn't important but relates more to spatial effects than the percussive ones you referred to, which is a source issue. Btw, some great quotes from JJ there and his linked ppt is even better.
If you can understand what he's saying (sorry Fitz), you'll see it aligns quite well with Dr Toole, Greisinger, etc.
It's like a blueprint on how to make speakers, being gifted for free.
How Ethan sat beside him and Amir worked with him....and still didn't pick up anything is beyond me....
As to Brians comments, well as you say those were old measurements...and still make no sense to me.
Ok, so to complete the thread jack, I'm guessing you took issue with Amirs poo-poohing of panels, but as I stated, those results are based on specific models with issues beyond the large radiating diaphragm and dipole>monopole bass integration.
Lastly what we measure with a single pressure mic sample at some point in the soundfield, is quite different from what we hear perceptually with binaural hearing. There is some relevant data there, sure, but limited. Things are a bit more complex that that, I'm still not sure what your "mono" measurement is showing, but for a panel with 180hz XO, a 1/6th octave resolution FR from each channel independently > 500hz or so is mostly what one would need, imho.
cheers,
AJ