I think it might depend on where you put your feet. Do you leave them on the floor or lift them on the end of the step? No matter what the height, I always keep my feet up because then I never arch my back. I know that's a big no no. So for lying down, I would say do what fits you best. Now for some of the standing stuff like one arm rows, I prefere 3 risers. I never do them kneeling on the step like Cathe has been doing because of my back. So I usually put one foot on. So once again, I think it's what most comfortable for you to keep proper form.