Regardless of outside space, the coop space minimum recommended space of 4 sq ft exists because during times of inclement weather, the birds are likely to hang out in the coop. It's during these periods that space is crucial. It's no coincidence that the number of threads asking about feather-pecking / bullying increases during winter time.
The more space you can give your flock, the more content they and you will be. I would never aim for minimum space requirements - I'd go for as much as I could practically afford.