Allow me Lon; thats the oldest trick, pull the backs off of thrift shop speakers and they sound great. I would assume it has to do with internal standing waves mucking up the sound. Reflected energy. You probably have cleaner, quicker but less bass now. Almost a Dipole. Face up I would guess eliminates early reflections and acts to diffuse the sound; like those who face their speakers to the back wall when they have a problem room. It's all in the Pi Papers from the Pi Speaker site. Free download.