Phil, my pipes are each 5' long - not through any carefully calculated design, but because I bought a 10' length of pipe and cut it in two. You think things through more than I do
. The distance between the tops of the pipes is just the distance necessary to make the fly sheet approximately taut - about 10'.
Because of the ridge line, it doesn't make much difference how high you hang the hammock in terms of flatness. This is because the ridge line limits how much you can "stretch" the hammock, unlike a conventional hammock. That said, the hammock is made assymetrical so that you can lie slightly diagonally, which allows you to lie reasonably flat and roll on your side. I find it quite comfortable (I'm 5'10", 170lb). With my current arrangement, I guess the hammock hangs about 18" above the hull with me in it. You might be able to lower the whole thing a bit, but that would make it harder to get in and out. I think it will all become obvious once you have the actual hammock and start fiddling with it.
I'm not in a hurry to get a SuperShelter. I think the climate here would be similar to Florida, so it only gets really chilly on winter nights. Never snows. I think I'll see how I go with just a sleeping bag - I'm more inclined toward camping in the warmer months anyway.
Here's a side view. The hammock is sitting up a bit because there's no-one in it.