It would be wonderful if InDesign could have a “floating” option for anchored frames the way that FrameMaker does: it allows one to define that, for example, an anchored frame would always be in the upper right corner of the page where the text flows that contains the anchor.
As it is now, if text is added above, the anchored frame moves down with the text, and if it hits the bottom margin, then text wraps to the next page without filling the previous page.