Dr. A (psychologist) from my college days had a desk and I sat on the otherside of the desk. He sometimes sat out from behind the desk but the desk was towards the center of the room and made it more intimidating.
My next T (Nov. 05-feb. 06) had a desk by the wall, a chair and a couch. If I sat on the couch, T sat in her desk chair and felt too far away from me. If I sat in the chair off to the side of the desk, T sat in desk chair and I crained my neck to look at her. She didn't seem to care how uncomfortable her office was.
My current T (Feb. 06-present) has a desk chair, chair, and a couch. When I first met her, I always sat in the chair by the desk and she sat on the couch but I ended up within inches of another clients file page. I kept looking at it and wanting to ask T to put it away for me all through the session. I never got the guts to ask her. I think I switched to the couch soon after that. I then discovered that all her degrees in on the side of the room where the chair is. So when I sit on the couch, she sits in the chair with her degrees on the wall behind her head. I then found that I was probably sitting where she usually does and didn't even know it. I now sit on the couch. I have thought about laying on the couch but wasn't sure if she allowed people to put their feet on the couch (I walk over to the hospital to see her. So, my shoes might get dirty from the sidewalk, crossing streets etc). I ask her about laying on the couch towards the end of a session, she said that noone tends to do that but I can if I want to. (I pretty much ask if people ever lay on the couch. I still chicken out of asking for favors from T and others) I haven't ever taken her up on the offer.
I have had some fantasies of hiding under the desk or curling up into a fetal ball. I find that a fetal ball position is a rather soothing position for me. It makes me feel safe.