i do not use heel/toe to help braking...that's what the brakes are for
heel/toe is used to get the car in proper gear for acceleration as smoothly as possible
heel/toe isn't actually that way...my foot can't twist to do that...so i wear sneakers and roll my right foot to the right to touch the accelerator while braking...you have to adjust the pedals to get braking effect while giving the accelerator a little blip to match revs (after awhile you get a wear mark on the top right side of your sneaker from doing this...and you begin to notice it on other racers)
for instance...going into turn 1 at summit point...120mph...jam on the binders...engage clutch (push clutch pedal in)...shift into gear that i will want to accelerate through the corner in (2nd...hard right hander that sweeps out)...roll right foot off brake (while still braking for the corner) onto accelerater to blip it to proper rpm (you'll have to practice at what speed you'll turn at to find what rpm you want to do and how far you need to roll your foot)...disengage clutch (you are now in 2nd gear and preparing for full throttle corner)