I also enjoy tarpentry.  I have tie outs along the ridgeline on the "up" side of the tarp and that is what I tie to my main rope.  Then the tarp is hanging down from, not over, the ridge rope.  If you drape it over the ridge rope, you can stop the leak that comes with water running down the ridge line by tieing a bit of rag or rope ON the ridge rope, outside of the tarp or just under the edge.  When the water runs down the rope it is stopped at the rag/rope and drips off instead.