On top or underneath?
Somehow I now imagine a weirdo with filthy hair coming up on stage to manically exhale onto your Axe...Well actually, there's a fan, yes, but it blows onto the cpu (not "out of the back") so if the air around is hot it will blow hot air onto the cpu
+1I like the Axe-Fx at the top to be able to see its display better, and because the power amp's cables do not block access to the Axe-Fx's rear.
Coming in from behind is fun sometimes too.