FWIWFM I have my subs on the floor beside my Maggies. I have tried higher mounts (on concrete blocks) in the past but have not found a real difference unless the sub is crossed over fairly high (mine are at 50 Hz). I do not claim to have Gary's ears, however!
Magnepan's crossover recommendations have changed through the years depending upon the model. For now, I am using an active crossover, L-R, 24 dB/octave (4th-order) on high and low pass filters and it seems to do fine. Perhaps the biggest issue in crossovers is getting the phase right at the crossover frequency so subs and mains are in phase; that is probably why some overlap (or even separation) helps some systems. I am fortunate to have continuous phase control built into my subs so I was able to dial them in nicely.
Magnepan's crossover recommendations have changed through the years depending upon the model. For now, I am using an active crossover, L-R, 24 dB/octave (4th-order) on high and low pass filters and it seems to do fine. Perhaps the biggest issue in crossovers is getting the phase right at the crossover frequency so subs and mains are in phase; that is probably why some overlap (or even separation) helps some systems. I am fortunate to have continuous phase control built into my subs so I was able to dial them in nicely.