There have been feed rings and tubes listed somewhere, not sure if they worked.
You can't make the feed tube itself tall or it will chimney, as you found out.
The ring idea should work well for burning lumber scraps, but any sticks/twigs with forks or shoots will hook and jam.
A tube that is at least a foot up off the burn chamber should not chimney. Maybe add a tight lid on top to completely prevent it.
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