Derek from TheUltimateHang.com wrote up an article showing various hammock tarps and comparing how they cover a hammock

Not all tarps are created equal. Indeed, what appears to be one of the simplest pieces of gear, next to a basic gathered-end hammock, tarps end up being one of the most complex. On one end of the spectrum you have the very simple asymmetric or diamond tarp that boasts only two guy lines and two anchor points. I’m not even sure there is a limit on the other extreme end of the spectrum where tarps become walled tents with doors, multiple guy lines, side walls, and even chimneys for stoves.

To cover a hammock, a tarp should extend at least 6 in (15 cm) past each end of the hammock. For most hammocks, a ridge line of 12 ft (3.6 m) is more than enough for maximum coverage. Tarps with shorter ridge lines should be hung closer to the hammock for the best coverage. Hennessy perfected the asym tarp to cover a hammock when you lay on the diagonal. It’s the least amount of tarp for the most protection, but for some it’s bikini coverage. In some ways, the popular hex-style tarp is just an evolution of the simple diamond tarp where the side panels are cut off to reduce weight on the unused fabric. Personal preference and weather conditions are prime factors on how wide, angular, or fancy the sides of a tarp should be cut.

Derek added a great chart comparing 10 different hammock tarps. Plus a few illustrations to show to different coverage for these tarps. Read complete article on TheUltimateHang.com

Derek Hansen is a lightweight backpacker, Scoutmaster, and “hammock enthusiast” who enjoyed his first hammock hang at age 14 at the BSA Beaver High Adventure base in Utah. The hammock he used then was a compact net style that was strung up in an “Ewok Village” constructed from log platforms lashed up high in the pines. Derek rediscovered the wonders hammock camping 16 years later in Virginia, and has been avoiding the ground ever since.