Official advice - keep 2 metres apart. Coming across dog walking friends we find ourselves staying a conservative THREE metres apart to exchange pleasantries. Thanks to peer pressure even married couples unthinkingly separate to avoid a "gathering".
Good idea to arrange them on a hillside, it adds a lot to the composition. Yes, the dog walker's dilema, the further you stand away, the more they shout ! And glad to hear official advice is in metres, I heard that some British politicians were trying to bring back furlongs or chains or something.