"Analysing the lateral distribution of pellets in the shot cloud it was established that there are two independent distributions, that is the horizontal (x) and vertical (y) pellet distributions."

No kidding.

Choke effect does one thing that we can easily observe.

It introduces a velocity differential. The leading pellets are started on their way 50 fps. faster (or so) than the trailing ones.

This introduces a time of flight difference that is increased by aero effects on the deformed pellets.

So, vertical dispersion must take place due to time of flight differences.

This part, however cannot be true:

'The tighter pattern generated by 2 1/2” chamber length may be caused by the restrictive crimp opening acting like an internal choke.'

The shot mass is under heavy and continuous acceleration right to the muzzle. Whatever speed differential is introduced by the chamber cone must shortly disappear. The shot mass enters the choke as a cylinder.

"The price of good shotgunnery is constant practice" - Fred Kimble