A. go as low as I can while still on the balls of my feet or..
B. go lower than that by pivoting on the middle part of my foot (balls of feet raising off of machine as heels go all the way down)
If you use serious weight then it depends on the footwear; if you're using "running shoes" with a flexible sole then you will tend to collapse the foot, hard soles will allow you to stay on the ball of the foot.