I don't know anything about pipe making, but I have a few pipes that I refer to as "well engineered." Some of the characteristics of those pipes include meticulous attention by the maker to how well the tenon fills the mortice on the shank of the pipe. On those pipes, clearly the maker has cut the length of the tenon to completely (or nearly so) fill the mortice from front to back. In this way, there is no "expansion chamber" inadvertently left in the pathway of the smoke as it travels through the pipe. Also, my well engineered pipes have a beveled entrance to the stem, which I've always presumed made the contraction of the gas going through the pipe more gradual and less apt to cause condensation.
Further, there is a definite venturi at the exit of the stem in many of them. That is to say, the maker seems to have intentionally made the last, little bit of the trip that the smoke takes narrower -- presumably for cooling the smoke at the very end of its journey inside the pipe. This is at a point where any water that is condensed leaves the pipe immediately -- into the smoker's mouth.
It would be interesting to section some of the really good smokers to see the full profile of the passageway. Of course, no one is gonna do that to their best pipes.
My guess is that the really masterful pipe engineers (Eltang, Rovera, Piersel) have all kinds of proprietary knowledge about the dynamics that occur in a draft channel on a pipe.
So, as I said, I don't know anything about making pipes, but I know I have some pipes that perform at a higher level than others when it comes to condensation, cooling, and aesthetic of the smoke that comes out of them.