If you're supposed to be sitting with your body as close to the tank as possible, then why would you practice braking with your ass as far back as possible? Remember good braking technique has you clamping your legs around the tank and keeping your arms loose so you can work at the bars smoothly. With your weight back you force weight onto your arms which makes any movement of your body affect the bike. Not the mention the fact you need the weight to transfer forward, so why would you move yourself back?
I'd also suggest staying away from a hard rear brake stab to start the weight transfer. Then soft to hard on the front while gently releasing the rear to prevent a pickup there. When you're almost stopped you can lay off the fronts and add some rear.