I found a couple of good images of what I think you're trying to articulate. One I've got in a book which has the archive #, but not being able to read German I wasn't able to find the picture in their online archive (its Bundesarchiv MW369110) photo of u-74.
Though this picture shows exactly what he's talking about
:
Unless the people standing on the conning tower are all a foot taller than the ones standing on the flak deck there is the 10" gap.