I have done A GREAT DEAL of shotgun-shooting over the years, between bird hunting since age 10--claybird blasting since age 14 (to stay sharp for Item #1)--and later as a lawdog and rangemaster for same.
IME. your results are a little "tight" for 10 yards--you do say "paces", so I don't want to split hairs here. Besides, a little "tighter" is better in my view. Generally, I have found in firing close to 250 different Rem 870 police shotguns--both bead-topped and rifle-sighted--that 1 yard of forward travel corresponds roughly to 1" of pattern diametric expansion. This is constant regardless of choke constriction with birdshot or buckshot. What changes is with increased choke constriction is percentage of shot found in the pattern center, which tracks smaller as constriction increases (to a point). Buckshot doesn't like full choke at all, from #4B to #00B. Modified is a bit better, Improved cylinder or cylinder is a toss-up for "best". Usually, makers install cylinder bore in bead-sighted defensive shotgun barrels, and improved cylinder in rifle-sighted barrels in the belief that IC does the best work with Foster slugs. My experience bears that out, but not strongly--it might be kind of a self-fulfilling prophesy made manifest by the presence of the better sighting tools. In the hands of someone who knows what they are about, either bead- or rifle-sighted shotguns are decisively lethal and sufficiently accurate to take out bad guys to at least 50 yards with Foster slugs. Just be aware that most bead-sighted shotguns--regardless of barrel length or choke constriction--are designed to "print" the pattern downrange somewhat high (relative to point of hold) because it is assumed that the shotgun is to be used on a moving target, and folks like to hold a bit below that target to track it more efficiently. Rifle-sighted shotguns, conversely, are meant to be used "point-of-aim = point-of-impact".
I enjoy handguns and rifles of most types, but I get LYRICAL about shotgunning. It is by far my best weapon.
