In my studio 99% of all portraits are done at a distance of 1.5 to 2 metres. Why?
In "Western" style societies this is the distance that two strangers set when they are engaged, interested, attentive, respectful, but not invasive of personal space. This gap is so familiar and consistent that facial features, ratio of nose to ears, chin to neck, etc, just look "right".
Once the distance is known framing is organised by choosing the appropriate focal length; long focus for tight face portraits, wide angle for half-figure, and so on.
I like this theory. I'm going to bring this in practice to see if you're right or not.
Thinking back on some of Avedon's pictures, I feel that wasn't always the case. Some are obviously in the 5 - 7 ft range. I don't have an example on hand at the moment, when I get to one, I'll give an example, see if anyone agrees.
Yes, Avedon frequently photographed with a Rolleiflex on a tripod, set up quite close to the subject. Prefocused, almost pre-framed. Avedon could speak with the subject, elicit responses, etc. even as he shot (with a cable release) and advanced the film without the subject being fully aware that the photo had been taken. You can see this, IIRC, on the American Masters show re: Avedon. (I'll confess that I can't quite figure out if he was using a Tele-Rolleiflex, or at times a regular Rollei with a close-up set. I'd tend to think the former is more likely.)
My subject-to-lens distance really depends on type of shots I'm taking. For portraits, I typically use 105mm. For half-length portraits typically ends up 3 to 5 meters, maybe? Closer (obviously) for tighter shots and farther for longer shots. If my intention is full-length only, then I'd probably use shorter focal length to keep things more practical - say 70mm'ish so I'm not megaphone away from my subjects.
Yes, Avedon frequently photographed with a Rolleiflex on a tripod, set up quite close to the subject.
Avedon usually has a dialog with his subjects so I would think working closely. While photographing The Duchess and Duke of Windsor at New York in 1957 knowing that they were dog lovers, he commented about a dog being run over to the couple then snapped the shutter. He made it all up to get an unflattering look on the couple's face.