No more Plant stalk

Robert Plant got a restraining order a couple of weeks back, to stop a woman from coming within 100 yards of him. Now, he's gone back to court and had that upped to 300 yards.

I'm sure it's reassuring to Plant to have this distance, but 300 yards still doesn't seem like very much - it's less than a fifth of a mile which, with the wind in the right direction, would be enough for Plant to hear someone shouting "look over here, Robert".

The distance seems to be arbitrary and short - it's roughly the distance between Covent Garden and Leicester Square. Is there a set of rules for working out how far the safe distance should be set at?