When my brother and I go backpacking sometimes we rig our hammocks with one above the other. If each hammocks head is on opposite sides they can be fairly close to each other with ample room to get in and out. Just hard to do with built in bugnets.
I and a friend have done this. It works fine. It's only a bother to the guy in the high position. We did rock,scissors,paper 3X to see who got the top bunk. I lost and just used my pack to stand on to get in. Was lots of fun getting out at 3am to water the plants.
I got in a fight one time with a really big guy, and he said, "I'm going to mop the floor with your face." I said, "You'll be sorry." He said, "Oh, yeah? Why?" I said, "Well, you won't be able to get into the corners very well."