I like this explanation- "Here's what's happening, the plate directs a small amount of incoming air to the flame where it gets used in the fire. Key is it keeps loads of cold air from flooding in & cooling the pot."
It's esp. true if your windscreen has lots of airflow, so you get convection drawing in more cold air than is required for combustion, which would cool the hot gasses as they rise up the sides of the pot. I've had the thought to try something like this out, but never did for 3 reasons, lazy, lack of free time, and it looks like it would be awkward to pack, but that could be overcome. Mostly for the first two reasons... I did do something like that for my wood-gas stove though, which I've only bench tested...