As mentioned, what you're seeing is the stock setup. Not sure why Ford thought it looked good that way. You can get 10'5" or 11" rims for the back that fill up the wheel well. You'll have to get a narrower rim on the front to pull the wheel back in.
My Cobra does the same thing. I haven't measured to see if the track is actually different front to rear or if it's just the body tapering towards the front, but it has always bothered me too.