OK, fair enough. Limitations of the firing range. Understand.
I'll take a stab at it.
Since I don't know how wide the paper is, I'll assume the boxes holding the corners down are shotshell boxes at roughly 4".
1. The pattern is very well regulated left to right. A change in velocity of your shells may change that slightly. I'd say the velocity that you are using is what the gun was regulated for.
2. At 25 yards, your shot has lost about 1/3 of it's initial velocity. At 40 yards it's lost very near half. It takes as long for the shot to travel from 25 to 40 yards as it does from the muzzle to 25 yards. It will fall about 1.5" from what you observe at 25 yards to 40 yards. It will fall another 3 inches or so at 50 yards. This is why the 'sighting system' such as it may be gives all firearms an initial elevation above line of sight. Shotguns are normally expected to shoot to point of aim at 40 yards.
3. Considering the above, I observe about a shell box and a half elevation at 25 yards, so it shoots 6" high or maybe a tad more. At 40, it should be about 4 to 5" high, and just about to cross the sight line on the way down at 50 yards.
It looks like a full choke to me, and shoots just where I like a gun to shoot.
The deceiving thing is that the 'peak of the crest' must be about 25 yards and it's all downhill from there. The shot travels from 40 to 50 yards in the same it took to go the first 20 yards. The drag on small pellets is very high and even higher when they are smashed out of round.
A high shooting gun is your friend.
