1. Sag Factor: I think you may have a winning diagnosis here! A 30 deg angle from ground places tension equivalent to your body weight on EACH end of the hammock, so imagine what the force is when the angle approaches zero deg. I would look into that forst.
2. A question for those more experienced with thread injectors than I: Is using a "blaa-point" needle better for the fabric, that is, results in fewer sliced fabric threads than if a "standard" sharp needle is used?