If you are laying asymmetrically, your feet shouldn't really be that affected. It allow more material from my legs to the end of the hammock which helps to reduce or eliminate calf ridge pressure for me and it also keeps me in place. Your centre of gravity is in you upper torso, so it is not in the exact centre of the hammock. If the ends are hung at the same height, your centre of gravity will tend to pull you down a little to the centre. With the foot end higher, your centre of gravity stays put.