My seated ear height is 38 inches. The center of the AMT driver on my X3s is 46 inches high (they are on GAIA II feet). My listening chair (MLP) is 10 feet 7 inches from my speakers. I have no problems with any AMT driver frequencies, likely because of the wave guide. My understanding is that the AMT driver plays 1KHz and above. I play a lot of solo piano music (both classical and jazz). Plenty of notes above 1KHz with no issues. All three drivers blend very well.
Edit: If Clayton says ear height should be the bottom of the waveguide, I'm still a bit low. The bottom, in my case, is 41 inches. That's 3 inches higher than my ear height. I do not feel any need to make changes. Maybe, some day, raise my recliner 3 inches. Bottom of the priority list.
Marcus