As for connecting the tarp to this line, I think you'll find there is more drop when you climb in than you imagine, at least more drop than I read into your description <grin>, and that this approach is what the HH line of tarps use. Can be made to work it seems.
I went with a Whoopee system not the SLS. My first response to the sag thing was it ain't that bad but it's summer and my lines are long and the sides are up. Sag isn't a problem at those angles. When the sides go down this winter then the sag thing will become more problematic. So I had enough ASblue to whoopee and left my buried loops for the tarp just in case I want to put it there. I also made a line of 7/64 ASblue for the tarp itself. I had a line of para cord but it soaks water the AS blue don't. enuff about my junk Thanks for the advise Grizz you've added to my hike!