I've come up with a little stove, made out of a small mint tin, mild steel. It seems to outperform the Ion stove, which is slightly larger, but made out of aluminum.
I've got a theory, and have no idea if I'm right or not, that heat that is radiating out the side of the Ion, through the aluminum sides, is not serving a useful purpose, perhaps only heating up my windscreen.
My theory is that the steel one, due to lower conductivity of the metal, is keeping heat from radiating out the side as much, and directing it up where it is useful.
Like I said, I have no idea. Just wanted to test the theory.