Here's one more quick question before I do any more cutting. I've got Ray Caffin's caternary curve calculator, but how do you determine the optimal maximum drop in the middle? I know this depends on tension, less drop for higher tension, and more drop for less tension, but I don't know how to relate this to real life typical numbers. What would be a good all-round middle of the road drop for typical tension on a 12 foot ridgeline?

And yes, I know people don't typically put cat. curves in plastic tarps, but I think it will work, and I want to try.