First of all, unless you sleep with your head on the floor of the bathtub, you are not going to be below 'eye' level of the 4-5" bottom. Even then one of your eyes will likely be above it...
Secondly I think that there is enough give in the bathtub floor supports to crunch it down a bit. On my TT Moment, if I were to choose to do so, I could simply put a rock or a stick or my mat near the corner border and it would scrunch down the bathtub by a couple of inches easy. This is a byproduct of what is a pretty forgiving connection between mesh and floor.
FInally I haven't looked at SS1 (Franco? Anyone?) but on my TT you could cinch the tent wall up (or down). However, perhaps this is exclusive to Moment.