These stoves are tricky. The reason for 3 holes on the inside are to keep it from getting too hot, while the larger ring on the outside catches enough heat to let it fire off.
Tricky balancing act. If the holes are smaller, it blows less fuel, but holds more pressure which lowers the boiling point. I had a couple that would run away and blow flames like a blow torch.
I have tried so many designs its not funny. Some are perfect and very efficient for 1 cup of h20, like 1.5tbsp/1cup h20, but they do not work so well for 2-3 cups and visa versa.
I can make one that will boil fast and not so efficient or boil slow and more efficient. This is somewhere in the middle and it works well up to 3 cups of h20.
So far this one seems about the best balance, but it would be nice to build one more efficient, like a 2.5TBS to 2.5C h20. A lot of that has to do with the container too. This 24oz Heineken can is efficient on this stove, but my feeling is that a 12 oz can would work even better for just a cup. I tried this stove with my old sigg aluminum 2L pot and I could not get the same short cook times and moderate fuel use.
Although aluminum heats up quick, it also dissipates heat efficiently so when its a big pot, its going to be a lot less efficient.
An insulator around the pot would help if I can find one that wont torch.