I bought a roll of the stuff and after making a pot cozy, a freezer bag cozy, a sit pad, and reserving some for a possible 'under-the sleeping-pad' layer for winter, I had a bunch left over so I tried this very thing out using a penny stove, as well as a V-8 sized penny stove under a GSI pot that's 4.5" in diameter. Both melted the reflectix in less than a minute. You don't even need to have the flames wrap around and up the side of the pot. The heat of the chimney effect is enough. The mylar layer didn't melt as badly, but the bubble wrap inside was trashed, warping and tearing the mylar.
I made the windscreen with about a 3/4" gap all the way around, and extended maybe 2" up the side of the pot with a small gap under the bottom edge, held off the ground with paperclips.