Kovin, thanks again.
I compared both, full results
here
The few differences are
- "cover" and "read_metadata_from_opf", but I guess this is just because Calibre extract the files first from my epub.
- 0 instead 0.0 at CMD
- level1_toc/level2_toc: I was not able to tell my program to use //h:h3 or //h:h4, when I try this ebook-convert.exe creates a directory h3 and puts all the stuff there instead of creating a mobi file.
None of those seems to be important to the filesize...
There must be another difference.