ActionScript 3.0 :: Mouse Move Initiated Scrolling Math

I'm really not great with the math. I'm pretty close with the formula but my movement is still wonky and doesn't stop where it should. (Top and bottom of the stage, rather than scrolling into infinity). For example, I need it to work like the menu at this link: [URL].

Code:
import com.greensock.*;
import com.greensock.easing.*;
stage.addEventListener(MouseEvent.MOUSE_MOVE, Move);
function Move(event:Event){
var distance:Number = mouseY - (stage.stageHeight)/2;
var percentage:Number = distance / stage.stageHeight;
var targetY:Number = -(content.height * percentage) + content.y;
TweenMax.to(content, 5 , { y: Math.round(targetY), ease:Expo.easeOut } );
}

Test of my code is here: [URL]. My fla is also posted as an attachment.