Ok, as I suspected, and this is why I stopped using the fancy feast stove very quickly during my initial foray into stove making:
With a wider wind screen, about 4" tall, didn't have a wider 5" one, performance was not just bad, but truly dismal.
At 17.5 ml, 500 ml water with fancy feast reached only 168F.
The reason was totally obvious, because the flame is totally uncontrolled, it shoots up the sides of the pot, in a sort of interesting circular way, ie, the flame shooting up the side circles around the pot outside slowly, kind of groovy to watch unless you actually want an efficient stove, then, not so much. It was precisely this thing of flames shooting up the sides that made me decide to find a better way to do penny stoves, but the fancy feast stove is what it is, it can't really be changed, whereas penny stoves can be highly modified and tuned, the only limit is your patience and willingness to inhale too much alcohol toxic fumes during testing. Any time you see flames shooting up the side, you know that you are looking at an inefficient stove, because those flames are almost all lost heat energy, though it might be a fast boiling stove because of that in some cases where you trap that heat energy with a wall tall enough to funnel it in a bit, but at the cost of roasting the wall over time.
Even with the wider screen, and increased air flow to the stove, I still saw significant yellowing of the flames, which fits with the discussion of the two flame types these stoves use, the turbulence created by the tight jets of a penny type stove I guess mix in oxygen well. This compares to the almost pure blue of the penny stove jets, suggesting the penny is getting a much better combustion of the vaporized fuel, which I knew already, that's why I spent so much time fine tuning the design in first place, to achieve that end.
So that's that, either roast my wind screens and begin to approach the efficiency of a well made center flame focused stove with a fancy feast stove, or get truly dismal performance using a wider screen. With more testing I'm sure I can get a steady 22.5 ml 500 ml boil without roasting my wind screen with a narrow pot, but really, why?
My testing by the way is NOT done on a work bench inside out of the moving air, it's done outside in a space where the air moves a bit, so the tests are reasonably close to real life.
It was good to go back and retest, thanks for the excuse to avoid working on a tedious real job project, but the tests show me why I stopped using fancy feast cat stoves on narrow pots, honestly I wouldn't use them on anything if I want efficient burns, maybe quick ones, on a wide pot, yes, but not efficient. I should have videoed the wide screen burn, and then shown a video of a well controlled penny stove burn, there's literally no comparison at all, one is just a basically out of control flame, one is tightly focused jets that don't get too hot or large, and basically focus all of the heat right in the center of the pot. I have been carrying a spare stove just for the heck of it, a fancy feast, but I think I'll swap that to a penny stove, that would make more sense I think in terms of a spare, maybe with a slightly different burner hole configuration for difficult environments.