Until recently I was have a very difficult time finding a sweet spot in my ENO single nest. I was about to turn it into a gear hammock, but I'm just stubborn enough to keep going.
I finally found (I think) the right combo and woke this morning on my stomach (first time in a hammock). Lots of sag was the answer for me. For whatever reason, I have to put a lot more sag in my ENO than any of my other hammocks to get diagonal; probably about 40 degrees. I'm not sure if this would be as true with the double nest. Point is, play with the sag; it worked for me.