@Jellby
You are right the book that I used for the first test includes much errors. After your comment I open it first in Calibre editor and there where no important errors shown after test (only 2 parts to big) but after using pagina EPUB-Checker I was shocked. The error list was so long that I stopped the tool and the check in Sigil with the FlightCrew plugin results a similar error list.
Next test was with a purchased epub where I only removed the DRM and here was only one unimportant error in pagina EPUB-Checker. The first result was for the trash and I started to change some page definitions and after playing around a wile I was happy with the result. (see attached pictures)
I think your argument why you delinted the page size can't be accepted. No normal user will read a eBook in PDF format on a eBook reader if he has the epub. Normal use of a PDF is on a tablet, handheld or computer and in my opinion the eBook should look more like a normal book. That was the reason to not only change the page size to A5 (14,8 / 21 cm). I also changed the margin to 15mm.
For the moment there is for me only two question left
- Can I and if yes how define some different output size / style definitions like A4, A5 (German norm size for paper) for example that could be loaded?
- Is there a known tool that can fix errors without handwork in a epub?