I can get a good fire going with no problem, but after 5 or 10 minutes, it seems to die down even though it still has fuel. Seems to be a layer of coals on the bottom, a layer of non-burning charcoal next, and then a layer of (recently added) fuel that just smolders. At this point, there's not enough heat rising from the bottom to ignite the woodgas, so it just smokes.
Once it reaches this point I can't get useful heat out of it, although dumping it out on the ground creates an immediate fire

Runs long enough to boil a couple of cups of water maybe, but not to cook dinner.
Lifting it and looking at the bottom, it appears that fine white ash has restricted airflow through the 'fan' slots in the bottom. Perhaps the coals are not getting enough air?
Any relevant experience, ideas, or group wisdom?