The main reason that it's not an easy task to put the floating header on article pages is due to advertising. Article pages tend to have Google AdSense ads, and it's against their TOS to have the ads covered up by dropdown menus. Right now, the ads are strategically placed so that the dropdown menus don't intersect with them. However, this would no longer be the case if the dropdown menus could appear at any arbitrary height on the page. The second reason is because the medium rectangle currently scrolls vertically in a bit of a fixed position. It would be a bit of a challenge to get it to coordinate with the top header so that one doesn't overlap the other. More importantly, it would be a confusing UI situation to have two elements on the page in different locations both scrolling down at different places, not in sync with each other.