If someone has this firmware installed on a lower-resolution device such as Touch or Glo, could you post a screenshot of the first page of this test ePub please?
margintest.epub (it shows a thin rectangle filling the available screen area. Sideload it as an ePub, don't convert it to KePub.)
Take screenshots with and without the show header option ticked. This will let us work out the size of the header to allow for in the `ePub fixed/adjustable top/bottom margins` patch.
(Edit: Screenshots from other devices like H20 wold be useful too.)