Actually I think people were warned to specifically not insulate the top of the chip. I can't remember where, but I distinctly remember reading that a heatsink on top of the chip can actually cause damage. Maybe that was because the pressure of the heatsink can cause chips to come loose from the board or something, but I do remember being warned not to try to exhaust heat out of the top.
The packaging of these chips is tuned to have specific thermal gradient ranges they will operate correctly under - if you actively cool the tops of the chips it can actually end up damaging the chip/ripping loose lead bonds/fracturing the packaging because the temperature differential between the top and bottom of the chip is too large..