Elliptical trainer adjustment query

Hi there,

Could someone offer some advice to an elliptical trainer (and
exercise) newbie please.

I've recently bought a Proform 585EKG elliptical trainer. It's very
adjustable, nine positions for the pedals and three or four for the
upright. The question I have is what am I looking for when I adjust
the machine?

Presumably, I should be upright and comfortable, but is there more to
it than that? I have it set so it's as smooth as possible (and not
'bouncy'). I do find that after 15 minutes or so my toes go numb. I
wear 'running' trainers on it, but I'm unsure if the problem is with
the adjustment of the machine or my footwear.

Any advice you could offer would be appreciated.

Thanks in advance

Karen