oetzi- take a look at the way the ropes are attached to the hammock body in this shot:
I know it doesn't show it very well, but the length of each rope decreases slightly as it moves to the outer edge. I'm at work and don't have the measurements, but there is a small difference in length. In my experience, more important is the way they attach. When I tried attaching them in a straight line at a single point, I got results similar to yours. When I used the method in the pic, that uncomfortable ridge under me went away and the edges tended to stay more vertical than floppy. The more attachment points you put on there, the less rigid it feels on your underside. I'm still experimenting with this concept.