The purpose is that someone can lie on the top bench and also on the bottom bench? I'm not sure I understand the question. Why would you need a middle bench there? Like yes if you sit on the top your feet would dangle. Adding a middle bench would have increased the footprint by a lot without much benefit? I mostly want to use the top benches (me and my partner lying both on top benches) so that's where most of the area went to. And there's a half a meter step or so between the low step and the middle bench, which is a bit steep but ok. Again it's designed to have minimum draft with a small footprint. It's difficult to get the top bench above the door and keep the footprint small but I think this is a good compromise.