If you think about how nearly all loudspeakers radiate bass pressure waves, then it really shouldn't make much difference if the power amp is behind or in front of the loudspeaker as far as exciting tube microphonics.
Tube microphonics
Hello. I am using Audio Research Ref 750 mono blocks and they in front of my speakers but off to the sides. Someone told me on another site that if I move the amps beside the speakers and not in front of them , my system will improve immensely. It will reduce tube microphonics. What are your opinions of this and I just want to say that I’m very new to tube amps so this is something I never heard of before. Thank you all.