I have played extensively with my tangband trio 15 open baffles...the 8” tangband cross frequency and type being the variable.
My impression is that I get fatigue listening to them if I cross them too low...ie if I ask the Tangband to handle 300 hz up, it sounds great if it isn’t more than moderate volume, but gets fatiguing quickly as volume rises (past about -25dB)
The fatigue effect diminishes to the point where, at 700 hz cross, it is pretty much gone.
(Edit: I would ideally want to cross under 300 hz so the driver to driver spacing is closer to 1/4 wavelength...but this effect has forced me to abandon that)
The biggest difference there is the excursion demand on the Tangband, while it is delivering high frequency content. I concluded it can be crossed low if I add a tweeter to offload hf, but otherwise needs to be crossed higher than one might expect.
One diagnostic problem is that it is impossible to accurately measure distortion when the volume is loud, due to room effects...so I am guessing that it is mid-high frequency distortion that is causing the fatigue I notice.
Anyway, that’s my suspicion in my specific case.