oh, i hope i tried all navigation buttons on it, I think so!
the key mapping doesn't work. I applied it in section called pdf and epub and general, but the options for scrolling don't get more.
there is next page, next section, and forward but they don't do different things or do anything at all when set. but key mapping should work, for I set other buttons different and was accepted.
no need for cutting margins, the device, firmware does it well, it is just, when you scroll bigger than the width it is impossibly slow to navigate.
just thought, hoped on an expert here for quick help. but I already found, where this was discussed, must use google, maybe I find it again.