An interesting question [eye contact and physical "space"]. Unfortunately, it's another one of those subjects which are so ingrained into our daily life, we hardly think about it, until that invisible barrier is broken. Thus, it isn't something that we record somewhere, and future generations could study for habits peculiar to our time. (I might back off a bit and say we do study and record such things today, in a rather clinical matter; in JA's day they didn't have hordes of socialogists prowling about meticulously measuring our every eyeblink.) The best we could do is take note of when people from that period make mention of it, often in passing. Such things seem to be more commonly recorded by foreigners visiting England, or the English travelling abroad.

One place where it was acceptable was in dancing. Making eye contact with your partner, and the other dancers in the set, was not only acceptable, but it would have been considered rude no to do so. Another reason for its popularity.

I remain, etc.
Jason E.