Like moebow, I make a wooden template in the feather shape I want and bend the wire around it. The wire will change a little when it's heated so I do my final adjustment with the wire on the burner. Turn it on, try a feather, notice where it needs to be moved, flattened, bowed, etc and turn off the power. Make the appropriate changes when the wire cools off and try it again. May take a feather or two to get it adjusted right, but then it's good to go for as many feathers/arrows as you want.
Island, I put the concave side of the wire toward the fletch. Makes a cleaner cut on that side, I think.