Hi guys,
I am really thankful for all of your help and ideas - but in the end it's simple: The fork has an integrated crown, that's one point for not believing in a microspacer to lift the bearing. On the other side there is the frame/steerer tube, so there are angles, too.
The best (?) solution would be the exact same bearing with 1 - 1,5mm more depth, but unfortunally this size is a special one, I even can't find the original one over here in Germany.