Well, ambient wind would still pull heat out of the water from the external sides of the can. It may not affect the operation of the stove, but I'm pretty sure it would effect overall efficiency.
Hard to see what's going on in that boiler design. I'm assuming internal exhaust venting from the Kelly Kettle reference? I 've never played with that design, but always thought it looked promising from the "efficiency" perspective. Just not very replicateable though IMO. I'm more into the "teaching a man to fish" outcome than running a kickstarter project, but that's just me of course.
So anyway, since we've got a little wind today and the temps are finally above freezing, I ran a single (failed) test out on my screen porch with all my current parameters (500ml water, 15ml fuel, 65-70* materials). It's 43 degrees out for air and surface temps (concrete patio block) with 64% humidity. Breezy enough to make my wind chimes play, but no idea the gust speeds, etc. I only was able to get 190 degrees out of the water, so I'd have to increase fuel to get a good and proper efficiency rating, but to extrapolate from the formula by altering the upper temp goal accordingly, it comes to about 47% efficiency.
Since it's dark out, I could see that the flame burned quite well and I even had an extended burn of almost 9 and a half minutes, probably due to the high humidity, so it's good to see my windscreen working effectively, which, after all, is what started me on this whole thing in the first place lol. It's pretty amazing to see how much heat gets drawn out from the external sides of the can due to exposure though. A taller windscreen would certainly be beneficial, but then I'd be back to square one on packability. As I mentioned over in my thread, I've kind of reached a compromise (at least for now) of geometry for my needs.
Update: Ran some more tests today with 17 ml fuel, 32 degrees outside, all else the same. Getting around 53%. Fuel gets cold before I get a chance to light it, so some variability in the whole thing. Tried a cylindrical chimney from the top of the cone to the top if the can, to act as a double wall insulator in the wind, but it surprisingly didn't seem to effect performance any. Then again, without a steady wind and only gusty, it's hard to get reliable test conditions. So anyway, in the real world, even 190 with 15ml is enough to have a hot meal. Also, I now attribute the longer burn times to a cooler running stove, as the concrete substrate was still cool to the touch after a burn. I think additional insulation is unnecessary, but a baseplate is for multiple reasons. Conductive insulator, and thermal reflection for functionality, as well as ground protection against burn scarring (shelters, picnic tables) or unwanted fires in dry conditions.
This is the chimney I mentined. (10g)
Oddly it had no meaningful effect.
As far as weight for just the boil system alone, I'm at 69 grams with stove, baseplate, windscreen, pot and Fosters lid. I could shave 5 grams by replacing the lid with one made from flashing, but it's not as cool looking lol