You should plant your last step more open to get away from rotating when throwing a FH. This opens up the hips allowing for your opposite shoulder to swing through, and then whipping your throwing arm through. What I typically try to mimic is a baseball player throwing across an infield. I grew up playing baseball, so this analogy worked best for me, as it is more or less the exact same thing. But, if it's more or less a routine ground ball, the lead foot is pointed toward the target, or at an angle just inside of that. It allows for a better weight transfer, and opens your body up to allow your arm a clear path at the target instead of throwing across your body.