Yes I find you need to be applying a reasonable pressure to the brake in order for it to be effective, the reason being that when swinging your heel round for the blip, you loose the pivot point that your heel was providing while on the floor. Trying to regulate the pressure effectively with a free floating limb subject to braking G-forces is what makes this difficult. When hammering hard on the brake, you regain the pivot point to some extent, albeit on the brake pedal and not the floor, this is why it is easier when driving harder.
I have now resigned 'proper' HT for balls out blats and trackwork, however an adopted technique of rocking my foot left and right whilst placed in between the pedals (works best with wide skate style trainers) works much better in day to day driving as you maintain the pivot point on your heel and so can effectively still regulate the pressure between the two pedals.
HTH