I haven't read all of the posts above mine so I am sorry if I repeat something. Foot positioning in my opinion is what your comfortable with. One thing I can recommend is that no matter where your feet are on the pedals, its more important to be using your legs to drive the back-end into the ground in order to keep a solid base.Your feet do no need to be super vertical to do that. Keep trying new things, within a logical limit, to find what you find you like.