As already said, personal preference. I tie some with a strand or two that are 1/2" longer than the tail, or 2 or 3 the same length as the tail. I will tell you that I tied one with about a dozen strands of crystal flash, figuring more was better. Haven't caught a fish on it yet. The stuff is pretty rigid with that many strands together. I also change up the look by adding it first, before feathers or hair, or by adding a strand as I tie now and then.
Creativity is just intelligence fooling around