Using tube amp upside down

I have a DIYish stereo tube amp that has the common tube amp layout: output and power transformers along the back row of a metal top plate, and quad of EL34s in front, and point to point components underneath.  The sides and bottom of the amp are essentially a wooden box, similar to Bottlehead amps.

I found that my amp sounds much better when placed upside down, resting directly on the output transformers.  I am assuming that when using the amp right side up, the wood sides and bottom that the amp rests on are adding resonance that does not gel well with my system.  Various decoupling footers and cones that I tried do help, but turning the amp upside down removes all this from the equation and sounds the best.

I am supporting the transformers with cones which also allows plenty of breathing room under and around the amp.  Is there any harm in running an amp like this?  I recall that some guitar amps have their tubes mounted upside down, but I have never seen a hifi amp with this configuration.  They always have the tubes sideways or right side up.