I've got a denon 3802 on my equipment rack. It's got about 1.25 inch of clearance on the top but a good amount of clearance on the rear and front. The manual recommends 4 inches or more of top clearance. Is this really necessary? Will housing my receiver in this condition cause a shorter life span due to over heating? After about a couple hours of play, the receiver gets pretty warm to the touch... not hot but pretty warm.