Comment # 5 on bug 1015478 from Johannes Meixner

Without a PPD the print queue does "raw" printing, cf.
https://en.opensuse.org/SDB:CUPS_in_a_Nutshell#.22raw.22
which means no filtering software is run on the system
where the print queue is - instead the print job data
from the printing application is sent directy as is
to the printer device.

Accordingly this issue is not an issue in the printing
system (i.e. CUPS plus filters and printer drivers)
but either an issue in the printing application
or an issue in the printer device.

Some guesswork:

I guess what looks like an a4 PDF (from okular)
is not really A4 but a bit larger and then in the
printer device it gets downscaled to get the whole
content within the imageable area of the paper.

See the documentation of your printer device
how it behaves when it gets contant that does not
fit within the imageable area of the paper and
how you can adjust that printer device behaviour.

Regarding things like imageable area of the paper see
https://en.opensuse.org/SDB:Landscape_Printing
which is in essence about the same issue:
Content does not fit within the imageable area.

The crucial part is to find out whether or not
the application's PostScript or PDF output
that is submitted to CUPS for printing
fits in the printable area of the particular printer.

In that article see in particular the section about

Debugging issues with "landscape printing"

It describes how you could get the actually
imaged/printed area of a PostScript or PDF file
by using the Ghostscript 'bbox' device that shows
the actually used BoundingBox (and not whatever
possibly wrong value a BoundingBox comment in the
file or other things like that may tell).