I don't have enough experience hanging in the rain to comment about the angle. So far when I have used mine it wasn't pitched real steeply. Water would hang around quite a bit before pooling and running off.
I also hang my tarp under the ridge line with a prussic on each end to move the tarp along the ridge line to where I want it more easily.
On my experiment with the thinner silicone, my scale wasn't sensitive enough to measure the weight gain accurately. It went from 10gm to 11gm, but it needs another decimal of accuracy. I bet it is very close to commercial material.