We've tested both large and smaller Martin Logan dipoles in the same room and got similar results. The listening test results are completely predictable by the anechoic spinorama measurements: poor octave-to -octave balance, resonances that are visible in many of the curves. The speaker is very directional and the balance changes as you move off-axis. It seems to sound worse as you sit more on-axis (it is too bright or harsh in the upper mids) but even off-axis, it sounds colored.
I have written about the subjective and objective measurements of these two loudspeakers: here (
https://seanolive.blogspot.com/2008/12/part-3-relationship-between-loudspeaker.html ) and here (
https://seanolive.blogspot.com/search?q=Kids). The large ML ($11k a pair) is depicted as Speaker M in the first graphic below. In the second graphic the smaller ML ($3600 a pair) is depicted as speaker D. Both speakers were rated quite low by a large number of listeners. The subjective/objective measurements in the graph below are of taken from the video, which you can watch from the above link.
The back wall behind the loudspeaker in the MLL is NOT absorptive as you claim. It has drywall covered by black acoustically grille cloth to reduce light behind the speaker and make it less visible through the blind curtain.
The distance of the speaker mover from the back wall can be programmed in 1-inch increments from 0 to 4 feet, plus add another 6-8 inches to account for the gap between the mover and wall. So it comes close to your recommended 6 ft. The first wall reflection would arrive ~ 10 ms after the direct sound. So the issue you raise about distance from wall and absorption do not apply.
The listening distance is about 10 feet but we have evaluated it at further distances, and it does not better. As I said before, the off-axis positions improve the balance of the direct sound, and this is entirely explained by looking at the spin measurements where the early-reflection curves are more balanced.
I do agree that dipole speakers should not be judged based on the performance MLs. I'm quite sure that better designs would score higher in our tests.
We have tested speakers over the years that include dipoles (ML, Quad,) bipoles (e.g. Mirage), the AR Magic speaker where you could adjust the direct/reflected levels, Omni-directionals, and speakers with wide dispersion in the front hemisphere (BeoLabs with the acoustic lens). We have also tested some line arrays like the CBT Harman Kardon Radiance 2400. I have yet to find a case where the sound quality could not be predicted based on the spinorama measurements unless it had sufficiently audible distortion.