When you design the tenting between the two halves, have you thought about adding extra material over the top and adding some poles to hold it up to give you full sitting height inside in the middle?
It shouldn't be too hard to do that.
I do something similar with the bug netting that I use when I camp in my sidecar rig.
I made the poles out of some of those fiberglass driveway markers you can find at any local farm store with some metal tubing expoxied to the end of one of them, making a socket to join them together.
The center panel of my cover is a rip-stop nylon material to keep the dew off of me, with the curve of the poles giving lots of room inside.