My 1.7is don't sound even remotely the same sitting down or standing up, this is one of my main complaints about them. I haven't heard the 3.7i, but this effect did seem less on the 20.7, though honestly I only heard them once and I could be remembering wrong.
My 1.7is in one system largely sound the same standing or sitting.
My .7s, however, sound VERY different standing than sitting when powered by my Pass XA25 but NOT when powered by a Benchmark AHB2 either in stereo mode or a bridged pair. I’ve been looking for an objective reason for this stark, but not blind confirmed, difference. It was something I just thought was inherent to the speaker until the effect was totally or nearly absent with the AHB2.
My current theory is a change in the spectral output of the speaker caused by the particular power/impedance/frequency/distortion characteristics of the XA25 and the impedance and dispersion characteristics of the .7s. The AHB2 has a much more textbook perfect transfer function than the designed-for-character XA25.
I am not equipped to do a double blind test on this, but I have accumulated enough measurement information on the amps and very similar Magnepan models (I can’t find good .7 impedance, etc. measurements) that I can conceive of effects that should be audible even if the WAY they are audible is actually surprising.
I know a bit off topic, but the Maggie comments kinda opened the door.