The choke is what makes heavy wads work. As the shot load hits the choke, it is squeezed down, constricted on the sides, elongating it making for an extended shot column as it passes through the choke. The wads are momentarily constricted, held back, so to speak and the shot cloud leaves the muzzle with the wads lagging quickly behind it, not pushing into it as from a cylinder bore.
WWGreener's shadow graphs show this very clearly on page 586 of "The Gun and it's Development", 9th Edition. The pictures, taken at 25" from the gun's muzzles, show the card undershot wad from the cylinder bore pushing into the back of the shot column, expanding it outwards. In both cases, the overshot wad is well ahead of the shot column and is what disrupted the wires to trip the camera. The shot columns are pictured 1" behind the overshot wads. From the non-choked muzzle, the undershot card (between the overpower card and fiber wad) is the one pushing through the shot, with the fiber wad falling back at this point. Were this a heavy fiber wad instead of the lighter card as used, it would have expanded the shot cloud even more due to it's mass.
From the choked bore, the shot cloud is extending forwards with heavy centre concentration, with the undershot card just resting at the back of the shot column and losing speed. The heavier fibre wad is already falling an inch or more behind the shot cloud, with the thick card overpowder wad an inch behind that. It does appear a full 1/4" over powder wad was used, along with a 1/4" fiber cushion wad in both loads.
Note how nice and square the cylinder bore's load it. It is a as long as it is in diameter. This makes for a shorter, although a wider shot cloud.
In his text., Greener noted that some improvement in patterning from cylinder bores was made possible by cutting threads into the steel at the muzzles, however subsequent shots filled these 'threads' with 'dirt'(fouling) which reduced the improvement to nothing. He was talking of ctg. guns, loaded at the breech.
I will note here, that in loading the gun from the muzzle, these threads could easily be 'wiped' out so the 'improvement' of restricting the wads slightly would happen each shot. I would not do this if shooting patched balls from the same gun, as when loading, the patch might be injured by the threads.