Last time I had the problem I made a couple of trials, but honestly I do not remember if I tried with the “print original size” setting.
But the point is that it should not make any difference. Well, it obviously DOES make a difference, but not to the extent I am seeing here.
I have always used the “Fit to printable area” setting and the results were correct for me. And I have not recently changed my printer or my printer driver.
As I said in the original post, the difference in size is huge: it seems it is printing to an A5 page instead of A4. That cannot be justified by the need to account for the unprintable areas.
And printing with lpr and the option “-o fit-to-page” does not show the wrong behavior.