I have been struggling with fixed positioning in iPad for a while. I know iScroll and it does not always seem to work (even in their demo). I also know that Sencha has a fix
position: fixed does work on android/iphone for vertical scrolling. But you need to make sure your meta tags are fully set. e.g
Also if you're planning on having the same page work on android pre 4.0, you need to set the top position also, or a small margin will be added for some reason.