The nice thing about the "basics" that I've described (low to moderate flame, use a lid, use a windscreen) is that they can be applied to pretty much everyone's set up. In other words, you don't have to buy any new gear to implement these (well, maybe a windscreen).
I completely agree with you that there are additional factors. A pot that is wider than tall generally is more efficient (unless you're talking about something like a JetBoil or Reactor pot with a heat exchanger).
Even more efficiency is obtained when one creates a set up where exhaust gasses are entrained such that heat transfer is maximized. Controlling the flow of the exhaust gasses is the "secret" to the efficiency of stoves like the Caldera Cone, Trangia, and Reactor. I've seen test results indicating that efficiency suffers less on high flame with such a set up, which would tend to corroborate your results.
Adventures In Stoving