A piece of terrain is 1cm high. My unit A is on top of the terrain, prone. My opponent's unit B is at ground level, standing, with LoF to A. So, A is above the bottom of B's silhouette (which is at ground level), but below the top of B's silhouette (which is 25mm above ground level). Is B in a "lower position" than A for the purpose of A getting cover pursuant to the prone rules? In other words, is "lower position" measured base-to-base (A's base is above B's base) or would A have to be entirely above B's whole silhouette for A to get cover? I feel like it's probably been answered before, but as usual my forum search term skills seem to be inadequate.