We never had a large number of game fowl keepers in our area, but had several walks around a county block (1 square mile) where walks ideally where at least 1000' apart. Drift was not a big deal with the brood fowl, but later in the season young birds could be a problem if flocks disturbed by a dog or a fence row was bushy enough to entice birds to walk further along it.
I had fun keeping walks closer but had to have a bushy fence to be a territory boundary or ranging areas were in opposite directions from roost as promoted by cover and other resources. Still, each flock had to have a few acres centered on the roost or trouble was likely.