Getting High Efficiency on High Fire

Looks like the colder weather in on it's way. So far I think I have my KA6 running good on the low end. Water temp goes down over time, my fire doesn't go out, and my ash had only a few black spots. Not sure if that's coal or stone. Anyways on to what I'm really asking.
How do you get your most efficient high fire? I know mine they say about 2" of dead ask. Feeder nut 11 or 12 on rice coal. So should I set the nut and try just adjusting the air from there? How do you get yours burning at it's best?

Generally speaking, you want the steady-state fire to end just prior to the last set of air holes on the grate.