My main familiarity is through nature programs on TV and direct observation. Ducks are relatively easy to watch at this time of year and they crtainly take the male-on-top position - in the water (to the point where the female is almost entirely submerged). The avocets I saw on TV - stilts are also wading birds but with even longer legs. Some birds do go face-to-face in courtship displays but I've never heard it said that they actually mate like that.