I treat the 4 sq. ft in the coop and 10 sq. ft in the run as a guideline, but I have not yet gone below that guideline. The way I see it, when on the roost there should be enough space available for birds that don't get along to stay out of each other's way. I figure that the roost length associated with a roomy enough coop takes care of this. The 10 sq. ft in the run, I believe, is the area that allows for adequate separation when outside of the coop. My birds do all get along, but I could not have known that in advance, so I followed the suggestions.
I also believe that ample room allows for enrichment. If you've ever gone to a zoo and seen a human object like a toy, or a creative way of offering food, that's enrichment. It's what zookeepers do to keep the animals actively angaged in their surroundings. Boredom is not good for confined amimals, including chickens. For chickens a large enough run area, ability to free range, or the change that comes along with relocating a tractor provides opportunity for something 'new' to come along and spark interest. Balancing area and enrichment has worked well for my flock.
So, what about an urban setting? I'd say that were I in that situation and using a coop I would consider the suggestions of 4+10 sq. ft first. If I couldn't meet that, then I would plan to add some regular enrichment. Dustbath areas, forage areas, oil seed tucked into nooks and crannies and perches in locations around the yard. Busy chickens are happy chickens.