I would hazard a guess that your foot position for normal braking is more aft than will be ideal for rev matching. By that, I mean that you probably use more of your toes and some of the ball of your foot to apply pressure.
For rev matching I would recommend the majority of the pedal pressure be applied with the ball of your foot. That being the case, I would suggest that you start out by moving your foot forward on the pedal under normal braking. When you apply the brakes, curl your toes *up* a bit using the ball of your foot directly below your big toe to apply 90+ percent of the braking force. Once you are comfortable with that, relax your toes and do the same thing while sliding your foot to the right. Eventually you will gain the feel of using the ball of your foot on the brake and you will find that a third to half of your foot is "hanging" out over the gas pedal. Once you're to that point you are almost home. The only remaining technique is to roll your ankle out a bit, using the outer portion of your foot to blip the throttle. Blip depth, length, and timing will take a bit of practice but once you have the basic mechanics down you'll be surprised how quickly they come to you. To really get timing down, as others have stated you will need to practice on a track as brake pedal depth will change dramatically under heavier pressure requiring less of an ankle roll for the desired blip.
Good luck and let me know if this helps!
2003 SGM SMG - Sold but not forgotten!
2010 JzB DCT - Lovin' it