I've gotten such a wide range of recommendations...
From your POV, the minimum sqft in a run is 10 sqft per bird, then? How flexible is this number if the birds will be free ranging at least a few hours each day?
You're going to see a wide range of numbers because some people do have chickens in a smaller amount of space without issue (in some cases, you have to consider scaling... a person with 50 birds in a coop that "fits" 30 may have fewer space issues than someone with 5 birds in a coop that "fits" 3, due to the fact that their overall space is proportionally bigger so they have a little more leeway).
The general recommended minimum run space here is 10 sq ft per bird. Personally I feel the minimum is, well, too minimal, because in an ideal run, there's clutter which eats up space, as well as adequate open space for birds to spread out and minimize conflict. But I know in a backyard setting with restrictive ordinances it may be very difficult to provide them much more space. Free range time does help but realistically the birds are still spending the majority of their time in the run - it's not like a dog where if you give it a good long walk it'll tire and relax for the rest of the day.