I'm 5'10" and have kids seats in the second row so I can't knock those down so easily, plus my back cargo area is usually loaded with gear. But maybe moving that gear out is arguably easier than setting up a normal tent.
Any comments on much sleep space is available with the second row seats still there?
With second seats in and not folded, enough for your hobbit friends.
Otherwise, a little over six feet with the second row folded.
We like the DAC tailgate tents also.
I think I went with a medium? The 80 is right on the line in terms of width according to how DAC sizes them IIRC. Ours was a little tight, so I added a "pocket" for the tailgate, plus a flap that keeps air from blowing under the truck and into the awning, which we set up like this. The profile of the DAC ends up somewhat different if you take this approach. It's more "closely tailored" but you have to sew to really make it work. I hate sewing.
We have panels to completely enclose things, but sometimes its just a quick overnight, like after we found the rocks at Point Abbaye a bit too fresh for camping, so we retreated to the parking lot before my Edmund Fitzgerald flashbacks got out of control.