Thank you for your clear answer. I didn't know all of this.
You're right to say things would be messed up if you change the font size, then you'll lose the page number references ...


A good workaround would be :
to put an index after the page number as the ebook reader of calibre does: p.10 > p.10.5 > p.11 ...
Or to have two type of page numbering: the absolute and the relative (to the configuration)...

Still as far as I remember, FBREADER for android does this. the page number depends on the font size and the resolution of the screen. The page number depends on the device and its configuration...

Thanks