There's no way to tell by looking at the window sticker. You have to see the actual invoice that the dealership has. They have the X plan, and A/Z plan prices listed on it. And, that price might vary according to where you live. Just ask to see it, they will show you.
I'd skip the X plan all together, ask to see dealer invoice. I typically start around $500 under invoice and start from there. There is holdback under invoice typically around 3 percent. They'll tell you their losing money blah blah when in reality there making around $400 at that much below invoice. I'd never pay much more than a few hundred over dealer invoice for a car.
I don't know the particulars but there are other incentives ford pays it's dealers. So don't fall for the we are losing money game at invoice price. The last two mustangs I've purchased were very quick, be informed let them make a little money and everyone is happy.