That is unusual. I wonder what else might have been going on. I started out with a flock of 15, coop 60 sqft, run 80 sqft. They free ranged some, not a lot because the guard dog was still in training. Then we burned down and the chickens had to get evacuated to a friends farm for a couple of months, then moved back to their coop and run. So lots of stress. Then they had to be confined to this set up for about three years. We had no trouble at all. These were RIR, Wyandottes, Welsumer, BR, SS, SFH, Brahmas. I tossed an armload of greens in the run every morning and that was all the entertainment they got.I hate being a downer, but I do want to relate my experience. I just went through my first batch of 4 (2 Australorps and 2 Rhode Island crosses). They had a 9x12 pen you can see in my profile images. No free-ranging, but we made A LOT of effort to provide enrichment. 7 months later, I have no chickens. They all turned on each other, likely from being stuck in close proximity.
Search for my thread “Breeds for Confinement”. Orpingtons are a popular choice. But from my experience, I would make the enclosure much larger, or find a way to contain them with electric poultry netting. A chicken’s purpose in life is to search for food, and limiting that will result in unhappy birds that injure each other.
Best of luck getting started with your flock.
The only time they turned on each other was right after the fire before we could get to them, when they were locked in a hot coop with little feed and no water for three days. Two hens were pecked bloody when we finally got to them, but that was extreme stress. Your set up sounds very adequate space wise for 4 hens.