Also for me the longer the better. I know Ed Speer says something like 2 feet over your height. I think I use closer to 4. Note that this doesn't apply to the Jacks bridge hammock, hh, or the Blackbird.
I would have to agree, a minimum of 2' over your height. I would also say 4' is more comfortable. I would think the longer the hammock the more flat you could lay except in the hammocks mentioned above by coffee. I use an ENO doublenest and would not buy a shorter hammock. The Jacks bridge hammock is the flattest lay that I have tried.