MM, I really think the difference in underhood vs. IAT increase in a linear fashion as ambient goes up If you look at my (!) chart, the HAI has the worst performance of the 3. It's (as you suspect) the big wad of plastic and its heatsoak issues that are the true issue.

The other issue is the torturous path the air must make on its way through that big wad of plastic. I painted mine pretty nice. Alaxfire has it hanging as art nowadays!