As with long tapered( or relieved) throats in modern shotgun barrels, I believe that the smoother and longer the taper in and out of the expansion chamber, the better the patterns. The long "neck" out of the expansion taper will do less damage to the pellets on the outside of the load, and give you even, ROUND patterns without strings or "tails" coming off one side or the other of the pattern.
Years ago, a friend of mine was given a specially made barrel for his Remington Model 1100 that had a long tapered Full Choke at the muzzle- 2 1/2-3" vs. 1". With certain loads he could get 90%+* patterns from that barrel. (* # of pellets in a 30" circle at 40 yards)
Coyote Joe's jug choke equipment( pictured on this forum several months ago) provided a much smoother and longer, tapered expansion chamber than you see in other designs. He could get more tightening of a pattern with less "pts. of constriction"( depth of expansion chamber) because of that. I believe his design also is responsible for his Jug Choked guns giving superb performance shooting PRBs, too. :hmm: :thumbsup: