The therapists I've seen usually have a chair a few feet away from a couch, or a couple of comfortable chairs where you can sit in view of each other, but at a comfortable distance and choose your angle. They usually give you an option of where to sit, but will usually have their own preference for the chair.

The whole chair behind the couch probably pokes fun at the old Freudian method of therapy, which was lying on the couch not being able to view the therapist. I think it's done in cartoons because people recognize easily that the scene occurs in the therapist's office.