Images on different screens

Hi Wes
How can I keep the parallax scroll effect while keeping the image fixed? or is it because responsiveness? Let me explain: if you go to http://elenabenitoruiz.es and you’re with a large screen and browser open wide, the slider image looks ok, but in some screens (especially letterbox, and the like), my head moves right where the main menu is. Is there any way to avoid this?

Thanks!