But, whenever I have used the HH stock set up, I am trying to avoid a good sized space between the hammock and tarp. I can get that space no problem when I tie to the trees. Then I have a nice tight tarp, and when I get in and it the hammock sags down, I have plenty of space above the hammock. And now I also feel quite exposed on the sides to wind blown rain. But, the tarp is about as tight and wind resistant as is possible with that tarp.
But when used in normal stock fashion, the tarp stays CLOSE to the hammock providing quite good rain coverage. When used with the SS undercover, nearly bomb proof. But then, of course, the tarp is now loose after hammock sag. Because, just like the hammock, the tarp is now closer to the ground. And no matter how tight you staked it to start with, it is now loose. So I use various tricks to help with that. Like filling empty stuff sacks with weight and hanging on the tarp side hooks ( what HH originally put those hooks there for), tarp tensioners, attaching wide and high(er) to trekking poles or branches etc. Definitely helps, but does not cure. But I have not had time yet to try your extra prussick technique.