most hammocks are 9-11 feet long.
I'm not sure you could get your hammock covered in a Dallas rain storm with a 5x8?
If you're going to make your own I would think something like 10x6 might cover you better.
Then you'd have a 10' ridgeline and 3' on each side.
I was thinking more of an asymmetric type of a rig. The diagonal would give about 9.5 feet, but it's the lack of side coverage that I was thinking would be the problem
The Integral Designs poncho is almost the exact same dimensions as the small stock hex tarp from HH. It is one inch shorter in overall length.
As such, I used it instead of the stock hex tarp on a couple of trips when I first started hammocking, rigged in the same flying diamond shape as the HH tarp. It kept me dry for a 6-day trip where it rained nearly the whole time. It does work.
The only problem is that, just like the stock tarp, it is so small all you can do is pull it down close to the hammock and stay inside whenever it rains. After 5 days of feeling gradually more and more claustrophobic, I swore off hammocks and didn't use one again for two years!
Now that I have a larger tarp, along with a hammock that allows me to sit up, I can enjoy the front porch & recliner effect that is such a joy after a day of hiking.
For shorter trips where keeping weight low is your goal, the poncho is okay, especially if it doesn't rain much. But when you're out for a long time, it's nice for your hammock to be your home, not just your crashpad.
I made one. Here is the thread.
Two things I see as useful info.
Big poncho, which can be too big for any bushwacking (kinda clumsy). It can be cinched up with the shockcords I installed.
Minimal coverage as a tarp, while it does cover my hammock, it may not work well in wind-driven rain. I have not used in a serious storm yet. I did an asym diamond like you mentioned. If the tarp is deployed, leaving the tarp is gonna be wet, since I wouldn't have any raingear.
If you look at Bonsai's video from the Hoosier Hang, you'll see me wearing it.
So other than those gray areas where it may be a problem, it can be worked around and perform the tasks as a double duty item. Using it as an endcap is nice too.
Ambulo tua ambulo.