Hmm...well there is a gap between the actual LCD and the "frame" it sits in. In other words, if I placed a piece of plexi glass on top it would leave about 1/8 inch but I don't think there would be much air flow since the case or frame is pretty flat as well.

I'm sure some heat escapes through the face of a monitor but doesn't most of it go out the sides and back where all the vent slots are?