It's a head scratcher, especially that dielectric that performed surprisingly well. As far as the metal of the pill and flashlight, I think it comes down to emissivity. I bet the best combination is something like this.
Use copper to quickly absorb lots of heat and conduct it to a layer of aluminum with lots of surface area. Maybe the current set up is good enough not to suffer significant sag, but this concept should increase comfort. Where lights typically only get warm around the pill, a longer copper sleeve would spread the heat more evenly throughout the body, which should decrease the heat felt at any particular area since there's more surface area of aluminum to dissipate the heat. Increasing contact area is already something lots of you guys do with P60's...and I'd do it too if I had any of those.