At the moment I believe that your astral body floats in your physical body or just slightly above it whilst dreaming and this also applies when lucid dreaming. I believe that unless you find yourself paralysed or in a state where you decide to project, then this will always be the case. I think that sometimes though for whatever reason, your astral body can slip away from your physical body whilst dreaming and its sometimes possible to tune into where your astral body is located be it consciously or not and then start wondering about from there. From studying the subject over the last few years and comparing with my own experiences, this seems to make the most sense to me.. for now.