I have a scrollbar that scrolls left or right when the cursor is moved either side of the central x coordinate. I've been trying to change it so the scroll only activates when the cursor is towards the far right hand side (ie x>75%) or towards the far left hand side (x<25%) of the scrollbar, leaving the central 50% of the scrollbar inactive. How could I go about this?

Code:
function scrolling() {
	_root.onEnterFrame = function() {

		container_mc._x += Math.cos(((mask_mc._xmouse)/mask_mc._width)*Math.PI)*15;

		if (container_mc._x>mask_mc._x) {
			container_mc._x = mask_mc._x;
		}

		if (container_mc._x<(mask_mc._x-(container_mc._width-mask_mc._width))) {
			container_mc._x = mask_mc._x-(container_mc._width-mask_mc._width);
		}
	};
}
The .fla is here http://board.flashkit.com/board/showthread.php?t=808636