My 1939 house has hot water radiators. They are only 6" deep, and in the living and dinning rooms are recessed into the walls so I have no incentive to replace them.
HOWEVER I have a small bathroom where even 6" is too much. Your knee hits the end when you stand in front of the sink. I'm looking for a flat version that would replace the existing one. I think I have seen them in Europe but is there someone on the East Coast that carries them?