People mud them to maintain that same airflow/shape. They mud on both sides of the shank. It's not necessary, though. It'll get the same way naturally, Sometimes I just put a drop of honey water on each side of the shank to accelerate things. Again, not necessary.Never done that. Although I do have two cobs (I think) where I decided to cut that little protruding section of shank out of the chamber. It’s unnecessary, and I wish I hadn’t done it. My others leave no dottle, but those that I cut always leave a small amount. They could probably use a little pipe mud in the very bottom of the chamber just to get the bottom level with the draft hole. Other than that, I haven’t seen a need for mud really, but hey, maybe I’m missing out on something. ?
Only thing necessary for a cob is to load it with expendable tobacco the first time. Smoke it hot, in the wind, blow down the bowl as if giving a "shotgun"... burn the residual varnish. Second bowl is greatly improved and things get real good after 5-6.