I've been spey casting for a few years and I've found lines that I like with each one of my rods but I've done through the process of trial and error. I'm trying to figure out how you guys figure out what head length and weight (grains) correspond to certain rods. I don't know if that made any sense but I just can't grasp how one goes about figuring what rod and grain weight match up correctly. What is the correlation? Does any of what I said make sense?