Lying on an angle to get a flat sleep is possible with almost any hammock, not just the Hennessey brand. The asymmetric part of their hammock is actually in the cut of the fly, as fair as I'm aware, and is a method of cutting weight by not having a fly to cover where not needed, if you lay on the angle. I've used two of their older model hammocks, they certainly are a good product, but I found the fly too small when it does rain, or if you want (for whatever reason) to lay on the opposite angle than the fly covers.

You could rectify that, if you found it a problem, by purchasing a third party fly with greater coverage, there are some good, and quite light, options available.