15" by 30"
Yoga blocks might fit, but would make the monitors too high. Right now, my face is the same height as the computer screen. It's very cozy. Walls behind me are 5 and 6 feet away, everything is very random and/or covered in cloth. The set up is facing the corner of the room behind me. I'm facing out into a largeish room. The monitors aren't for intense mixing. That's what the headphones are for and I prefer the headphones, but need a break once in awhile due to ear fatigue in spite of low levels. Right now, I have a pair of pretty generic Logitech computer speakers I hook up when I want them. The footprint is 3.5x4 inches.
I'm afraid you are over thinking this sitch, Chris. I'm not setting up to go into production. The goals are a better pair of monitors and the interface to bypass the computer's soundcard. It may be temporary. It still needs to be mobile.