Kinda nit picking but the "forcing cone" isn't found in the choke section of the barrel. The forcing cone is the area immediately ahead of the barrels chamber. Usually a more gradual and/or lengthened forcing cone patterns better because it allows the shot an easier entrance into the constriction of the shotguns bore. The bore is tighter than the chamber and the easier the shot can sort itself out entering the bore there will be fewer mashed pellets and less disruption of the shot. The more round pellets the better the pattern and fewer wide straying pellets flying off into outer space.
Extended chokes have a longer "parallel section." This longer straight section of the choke does about the same thing for the shot column as a lengthened forcing cone at the chamber. Only now the shot gets the gentle treatment at the exit end of the barrel. The choke constriction is tighter than the bore so it's the same process as from the chamber and into the tighter forcing cone area. Also, usually extended chokes have a wad retarding mechanism to slow the plastic wad from the exiting shot pellets. Not having a big hunk of plastic banging around in the back of the shot column disrupting pellets is a big plus. With standard wad systems stripping or slowing the wad from the shot column gives a much more consistent and center dense pattern.
That is unless you are using a Flite Control wad system like Federal and now Hornady use. In the case of the Flite Control wad it is designed to stay with the shot keeping the shot sorta gathered together farther down range before separation. Firing a shotshell using the Flite Control wad through a tight exit diameter wad retarding choke can be potentially dangerous by causing the shot load and wad to bridge in the choke. This would basically be about like firing a solid Foster style slug through an extremely tight choke. No good comes of that. Barrels bulged, blown or stripped of chokes have resulted from such a bad combination. However there are extended chokes designed for the Flite Control wad that don't have a wad stripping/retarding mechanism. By all accounts these specialty chokes work quite well.
