understanding the twist at the top.

I believe I understand that moving the fair lead back will cause tightening on the foot, and moving the fairlead forward causes tightening of the leech. So when you move the lead forward, your allowing for the sail shape to pooch or basically the curve between leech and luff to be deeper than it normally would be. Which is logical in light winds. Now for pulling the cars back aft, which would pull on the foot, this tightens the sail at the foot but I get confused on the shape it makes in the top of the sail or this "twist". Does this twist basically make the same deep shape at the top of the sail, or does it actually curve inboard on the leech of the sail? I understand how this causes ineffective use of wind higher up the sail, but trying to image what it would look like in real life. "In this case, in wind, the foot would stay taut and not move much but the leech would "twist" out and away downwind. This is especially prevalent at the top of the jib where there is little tension holding it in place."