Thanks Debi, Owl, and JayS! I was concerned that if the UQ didn't have a slit entry, it wouldn't sit in the right position after I got into the hammock, and then I wouldn't be able to adjust it from inside (except maybe near the entry). As Owl points out, it would seem that if the netting on both sides could be unzipped, it would be easier to reach out to make adjustments. But JayS suggests that an UQ may work fine without much adjustment -- maybe I'll try it and see if I can make it work before I jump into the zipper mod.
Debi, I hadn't realized that a 3/4 length UQ would clear the slit -- I've seen some 1/2 lengths that certainly would, but I should probably measure my HH so I know how much clearance I would have with a particular 3/4. That said, however, I really think I'm going to end up wanting a full length if I want to be warm enough.
BTW, I am intrigued by the HHSS. It's certainly lighter and much less expensive than most UQs. I'm just concerned that since I sleep cold, I'm going to end up wanting something warmer. Most of my mountain trips are in April and Sept, and nights are always below freezing.