If I'm going to the boonies, I think you are too close if I know you are there. Sight, sound, doesn't matter.
And I am certain that it is because many folks are afraid to be "too" alone. We once sold a house out at the edge of town, at the end of the street, almost to the cul-de-sac. Empty lot on either side of us, but a house across the street. Showed it to one family and mom turned to dad and said "I could never live in a house this isolated." I suggested a brownstone, but they said they wanted privacy.