By fly I assume tarp - I tend to have a 30' ridgeline (continuous) for my tarps. Seems to work for me. If you're not looking continuous simply subtract your tarp ridgeline length from 30' (or 25' or what have you) and put those on either end. I wanted enough to get around some fair sized trees.
The key to immortality is first living a life worth remembering. - St. Augustine
Some people feel the rain. Others just get wet.
- Bob Marley