Action script 3 mouse scrolling

programming flash
1

Hi guys
i have a problem with mouse scrolling.
I have movie clip which is smaller then project itself and i want to scroll it using mouse cursor…moving cursor down will move all movie clip move down. i have a code

var yRange:Number = ( ee_mc.height - stage.stageHeight);
var yMax:Number = ee_mc.y;
ee_mc.addEventListener(Event.ENTER_FRAME, moveEE);
function moveEE(e:Event):void
{
 var yPct:Number = ( mouseY / stage.stageHeight ) ;
 var yNumPixels:Number = yPct * yRange ;
 ee_mc.y += (yMax - yNumPixels - ee_mc.y) / 5;
}

and it is working perfectly…but.
You will see whole top part of the mc only when Your mouce cursor will be on the first pixel of the stage, the same thing is with bottom part.
I would like to change it somehow, that it will start to scroll down in 20% of the stage high and on 80% of the stage high the bottom part will be fully visible.

thanks in advance for Your help