i always think of this as actually changing the direction of the hair root rather than breaking the hair. this may actually be wrong, but the deeper the "break", the more effective, at least for me. if you watch people do this, the spray a little, comb, spray a little, comb. it takes a little practice not to put too much on. i'm pretty sure that girls and some boys that put on mascara in a nice even way are pretty good at legs.
i never got to use a roto brush and just always rinsed, brushed, repeat.
gonna start practicing this fall again. should be frustrating.