Eliptical Cross trainer foot position?

Hi all,
Just some advice for any fitness buffs out there. Picked up a very good deal on cross trainer. However the front of the foot pad (where your foot sits) is missing. When using a cross trainer where should your foot sit? From limited knowledge a while ago I thought your foot should sit centrally in the foot pad and that the raised area all the way round isn't used to aid with the exercise. If andbody could advise it would be appreciated