Thank you.
Setting scale inner, indeed cuts quite a few things away.
Interestingly, I now noticed that with the default setting: letterbox integer scale, when i maximize the browser in an external (24'') monitor black areas are mostly gone, but when maximizing on my notebook monitor (12'') thick black borders exist.
Not sure why this is happening.
Edit:
I see layout size parameter and viewpoint, which is also a 2D size.
Why do these two exist in the first place. Why isn't one size enough.
Perhaps because the layout is used for other stuff ...
So the layout size is simply a work area size, whereas the viewpoint is what is displayed -- which, i guess, means the aspect ration must be aligned with the actual aspect ratio of the monitor in use.
This may explain why borders appear on one monitor (with a different aspect ratio) than another.
So, how can a viewpoint be defined that seamlessly works across two or more monitor.