Hi, I am considering getting a open 4-shelf rack for my HT system. My receiver's height is 7 inches and distance between shelves is about 9. That is pretty much true for any rack available. The manual says to leave 4 inches above the receiver, on the other hand I saw a thread recommending putting receiver on bottom shelf. It is an open rack (just shelves and 4 beams), so air exchange is good, so would putting receiver on bottom shelf with less that 4 inches of space above it an overheating problem?