When i play heel up, my heels are about 2 inches above the ground, with all my toes flat along with a little bit of my foot, up till the bend. Anyway I control it centrally with my upper legs and use the 2 inches for a bounce if need be, my toes area always flat, my heel is never touching, always up, but bouncing. When i'm playing fast double kick i move nothing about my foot, my whole foot is tightened with the heels up.
I use this same technique but I have the tension on my beaters a little tighter. I get these unwanted doublestrokes with the tension too loose. Feels like I have no control over the beater.
-RHS