This could be very well true, thats why they prefer the aluminum covers because of the small chamber volumes, that cover will help act as a heat sink because I think you only have .25"-.375" clearance to the back of the driver. Not only that the high compression ratio in the throat of the horn, I think they said it was like 2.8 to 1. Some pro sound company measured the pressure in the throat running it at full tilt and the pressure in the throat was like 15Lb's per sq. in.. Also even though it's rated at 400wrms a driver, 800wrms total, pro sound guys usually run amplifiers at twice the RMS ratings of the speakers, and this is with hi-pass filters on them at 30 Hz. So yes I can see where this could cause a great thermal problems on the drivers themselves.