Somehow, I must have missed the posts before this. I'm glad the site didn't implode. And thanks for the kind words, Jeff!
I think you just blew my mind, Alan. :) I haven't run any tests to determine how complete the combustion is with the Boiler. It's kind of a chaotic system in there and conditions change based on the state of the fuel used as well how densely packed it is in the chimney. On one hand, you can break up some twigs very small and batch load it like is done with gasifiers, on the other, you can also break them up into larger pieces and add them as you go - that flexibility is something I think is a real advantage.
But getting back to your point, more complete combustion would increase efficiency, so would doing something like making the chimney another several inches taller. The latter would actually both aid in combustion by increasing the internal draft as well as catching more of the exhaust heat.
In the tests I did perform, though, I found that it took just about 2 oz (a decent-sized handful) to boil 20 oz (so a bit less for the now-recommended 16). The thing to remember about wood stoves is that since you don't have to carry the fuel, it's environmental impact rather than pack weight that drives you towards efficiency. Given how small this already impact is, and that almost any measure to increase efficiency would add weight or complexity, I went the way I did.
But would I like to see a gasifier kettle? Heck yes. I bet you could just toss the kettle on top of a Bushbuddy...