Having said it once, he never says it again. Thetans as badly off as human beings do not feel particularly distinct from their bodies. This is a subject of amusement to L. Ron Hubbard. He regards anyone who is not thoroughly aware of being a totally distinct entity as being something not quite up to the level of a village idiot. In Scientology though, thank goodness, a goodly proportion of us can readily find out that we are not our bodies.
People actually do it.
They don't just imagine they are three feet back of their heads. They don't just adopt a viewpoint as if they are three feet behind their heads. They are actually in a position exterior to their heads. At least, according to L. Ron Hubbard they are. How one can demonstrate where a Thetan is at any particular moment when he is a nothingness is not very clear.