One year and 3 weeks since my last post to this thread! When I posted the first time I was fairly new to the hammock and hanging in my first DIY. Since then I've made 3 others and I'm now sleeping every night in that same original. The only structural change has been to add Redoleary's mini-spreader to both my nightly hammock and to the hiker recently. Which you will need to try to see the difference in the comfort of your hammock.
As far as a 'flat' lay in a hammock. Fact is you will never lay flat in a hammock.We're sleeping on a piece of fabric and the human body mass is around your belly button even on a sheet of plywood you wouldn't be flat, your posterior is going to be at the lowest point. My goal is a 'comfortable' lay. When I hit the hammock at night I do a little reading on my back, on a diagonal, feet and head slightly elevated. When waking for those night calls I may be on my back or half side. Never have been able to get fully on my side or stomach, maybe because I just don't bend that way. I can understand those who just can't make the transistion to a hammock, my wife can't.
It could be my that my hammocks are DIY's but I can't imagine any hammock being a perfect fit for everyone. I believe I tried every gather method and invented a couple myself before settling on one the mini-spreader. Calls to mind the saying " If at first you don't succeed... so if it doesn't work the way it was bought or made keep experimenting. One night you will hit the hammock and wake up late the next morning wondering what just happened.