I like to use a pot which is 8.9 cm wide (3.5 inches) - because anything bigger would be a waste of space and weight for my needs. It's identical to a Toaks 750ml titanium pot.
Most of the stove systems I tried, are inefficient with that pot since they produce a flame that is too wide, goes over the border of the pot, and wastes fuel by heating the sky rather than my water.
I am experimenting with some DIY alcohol designs to find which is more efficient with that pot, but I wanted to know if someone already made some tests and came to a conclusion.
I am quite skilled with DIY so a complex design wouldn't be a problem. Living in Europe, availability of some source materials, could (like, aluminium red bull bottles are almost impossible to find here).