I'm also downgrading to 2.5.1 because I don't like that header displayed above normal epubs.
I must say that I'm a little bit shocked that Kobo doesn't listen to members of the beta group.
Headers and footers- make the display of the header and footer optional and let the user decide to show or hide it. When hidden, allocate this free space to the reading area so more text lines are displayed on the screen (full screen mode).
- make the header and the footer smaller in size by moving the text in the header and footer closer to the edge of the screen without changing the font size. Using a slightly smaller font size for the footer text frees up even more space. Also the vertical margins of the header and footer are relatively wide and can be made smaller. To avoid compromizing the tapping area of icons these should be positioned/aligned horizontally slightly wider from each other.
Page margins- the user agent (ua) minimum page margin should be 0, as page margins are normally defined in the epub itself (by the publisher, and may be to big or to small, but are rarely 0.).
- the kobo ua offers to adjust the left and right page margin. Add this feature for the top and bottom page margin too.
At the moment the Kobo ua minimum page margin is > 0. When the left/right page margins are set to its minimum (using the slider) there is still a (default) margin. The absolute minimum margin should be set to 0 (see bullit one in the list).
I have no problem if Kobo decides to set their default ua page margin to, let's say 0.5em (let's asume that is Kobos current default setting) as long as the user can reduce this margin to 0.
Code:
ua page margins + epub defined page margins = displayed book margins