When the bar is touching the shin, and your hips a little lower, the bar will be over the mid foot - where indeed you want it as mentioned.
I also pull back not up.
Its not just a back exercise. Its also very much leg exercise. It is a back exercise in that it works the back side of the body - back, glutes, hams, amongst other musculature. Even a stiff leg DL works the hammies Alot - infact that is the point, also glutes as you should be consiously trying to use the these muscles right through.
To say its not a leg exercise is incorrect - if that is what you are saying.
But in truth, this lift(like the squat) is very different for everyone.
Tim.