I just looked at lot closer at the side tie outs on my HH ULBA.
The side tie out is reinforced with a material cut in a triangular shape. I think the material has two purposes:
1. reinforce the tie out, and
2. give the tie a predetermined angular shape.
Simply sewing webbing along the side for tie outs doesn't accomplish the second purpose. Rather, in that case, the angle formed by the hammock body at the tie out would be totally dependent on the position of the stake.
The reinforcing material forces the angle to be the same irregardless of exactly where the stake is positioned, within rather large bounds.
I think the reinforcing material acts somewhat like the structural ridgeline. The ridgeline determines the amount of sag. The reinforcement at the side tie outs is a major factor in determining the exact asymmetrical shape of the hammock.