Scaling background proportionally

I know how to scale a background normally, but what I am doing here is a bit different. I have my main background that scales correctly. I then have a second background that gets loaded when you select a sub menu. The background starts under the submenu however and this is whats throwing me off. If you view it here: and click aiman motor on the bottom right (wait for the second bg to load) you can see it is scaling, however I need it to stay right under that white bar (the sub nav bar), but its not. This is what I am using to resize.

private function onResize(e:Event = null):void
	bgHolder.width 	= stage.stageWidth;
	bgHolder.height = stage.stageHeight;
	(bgHolder.scaleX < bgHolder.scaleY) ? bgHolder.scaleY = bgHolder.scaleX : bgHolder.scaleX = bgHolder.scaleY;

anyone know a solution?