Air heating is good to arrange around the hearth, silo preheat starts at the silo funnel.
Air heating first, then silo heating in the center of the silo.
One does not exclude the other, they come in series.
And decent cool silowalls... in the beginning. Its under work.
Well, you don't get perfect wood in every place, but with a well equipped gasifier you will overcome the most usual inconveniences.
To me an easy cleanable air preheater is harder to design than the plank. Vertical tubes manteled around the hearth is the current concept. Gas in vertical tubes, air around.
Sounds like the steam went out of you, rare!