Personally, I don't let the fly hit the water on the back cast. Kind of like using a fly rod, when you feel the fly give your rod a little tug at the end of the back cast, that's when I begin the forward motion. And you want to lob it out there, you don't want to create a whiplash effect on the forward motion. Takes a little getting used to, but it's surprising how far you can throw that light bobber and fly on a good cast.