@shadim sorry for the late reply but I had to travel abroad.
We used to save all our PDF label (which came out in an A4-like format) then printed them altogether setting “print two pages in one” option in the Acrobat print options. With this new layout (check link in opening post) this same workflow led to 2x A6 sized labels and 2x white spaces.
Following suggestions from other users, we have now tried 900-300-700 format and it seems to better fit A4 as the resulting label does not have empty white space, and just by being rectangular, it’s a better match to european A4 sheets. However, the setting in the plugin can still be misleading for most users.