XPA-200 ventilation requirements/recommendations

[gregd]

How much space should I have above my XPA-200 so that it has adequate cooling ventilation? It is in a rack that is enclosed on 4 sides if I put the door back on (I took it off when I rearranged things months ago and haven't put it back on). There is pretty good ventilation to the outside of the cabinet in the back. There is not much in the rack: XPA-200, XDA-2, a small Blu-Ray player, and a small atom-based computer.

Thanks for your help!