Perhaps the difference is the length of the rifled section. I have read that the paradox in some makes was up to 4" long. I do not know that for fact, but a shorter rifled section, as in a choke - perhaps 2" long might give better patterns, but possibly poorer accuracy.

Last DGJournal had an article by Ross S. in which he finally tested slugs in his 12 bore Lanscaster oval bore(& shot an elk with it). He reported a final group of 2 shots each barrel going into 2" at 100 yards - which is amazing accuracy for open sights - but then, he shoots open sights a lot & the practise sure helps.