I'm not much bigger than IAHanger, at 5'10" 150 lbs. I've been experimenting with this a lot lately, and I've found I like the ridgeline to be pretty taut.
I string it up so that the suspension straps and the hammock ridgeline are pretty level (nearly no sag) and then once I've sat in it, the sag is almost just like that photo.
The suspension lines get higher above the tarp lines progressively, as the trees get farther apart. The tarp lines stay at the same level (about shoulder height).
I don't make any claim that this is the right thing to do. It's just what I do.