Nice work! I've got a couple of DIY sil ponchos that are just the right size for that - I may add some perimeter shock cords. The 3/32" shock cord from Questoutfitters will fit their minitoggles - very tiny.
Do you carry a towel? I didn't on one trip, and I got caught in a fierce rainstorm, so I stopped and put up my tarp and hammock to wait it out. Then I realized that I was so wet I didn't want to get into my hammock. I used a shirt to dry myself off, but since then I carry a super-absorbent towel - actually a piece of "Zorb" fabric (used in diapers). I can also use it to dry my tarp when I pack it up in the morning. It would be handy to make sure your poncho isn't too wet when you hang it under your hammock.