Ex t swapped offices often because it was a community center with shared therapy spaces (there were 4 rooms we bounced between depending on the assigned office). They were tiny (kinda reminded me of closets) so there was never more than 3 feet between us. If the chairs were placed directly in front of each other, I would angle mine slightly off to the side. There was no real opportunity to "get comfortable" in those chairs. There was no real option but to sit upright.
Ex ex t's office had the choice of a couch or a chair. She would sit in her desk chair at an angle to either seating option. I always chose the couch because the chair would have had my back to the door (something that makes me very uncomfortable). I also prefer hiding in the seating option as best I can, so her couch was perfect: cushy, filed with pillows, and I would sink into it. It was nice because we covered very vulnerable stuff. I think all the offices in that center are set up less confrontational, more comfortable, and easier to hide in. They deal with child abuse and sexual assault, so I'm guessing they try to make it inviting and as not intimidating as possible.

I would agree that most chair setups are first dictated by space restraints and only secondarily by therapeutic impact (at least in community mental health settings. Private practice may have more flexibility in choosing office spaces).