That's a different question. If you are in someone's draft, you will almost always be faster than them, and when you pop out you will usually sling shot around pretty easily, but then slow down. If you want to hold your position behind someone slower, it is the same as being in a paceline: sit up or stick a knee out. It won't take a large change in surface area to let you modulate behind. Don't hit your brakes, just brake with air. Works very easy.