Rex, Yes, I have used similar. About 10-12 years ago I used a piece of aluminum foil over my pot(s) to capture heat from the old SVEA. It worked really well. But, as Roger says, you have to have enough air feeding the bottom jet and flame. This will keep CO emissions to a minimum. Since the heat will rise, out of the vents, I don’t see any problem with it in that regard. But, when I used a cone, it slipped off the pot. You can see the off angle it is sitting at in the pic. I am guessing that is due to the expansion and contraction of the metals. That is why I used a simple “cap” over the whole pot with an extra large piece of foil with some holes punched in it.
I added a found stone on top to keep it relatively in position, in any sort of wind. It worked pretty well actually. For about the weight of the top, it also captured the heat next to the pot. However, in any sort of wind, it would still blow the flame around a bit and really disrupt heat flow in the cone. So, I still needed a wind screen around the lower to prevent that. Carrying both turned into a gadget factory.