[Evolution] Adjusting font size of calendar display

[Axel G. Rossberg <Axel Rossberg net>]

Hi all,

I am using Evolution 3.18.5.2 under Ubuntu 16.04.

Recently I decided to set the font "Scaling Factor" accessible through
gnome-tweak-tool to 1.73, to make sure applications know the physical
size of my screen.  Then I reduced the size of the fonts "Window
Titles", "Interface", "Documents" and "Monospace" or 6 or 7, to
compensate for this.

This worked well, also for evolution, except that the font used to
display dates in the calendar (both side bar and main calendar) is
quite small (an estimated size 4 or so, compared with the other fonts
displayed).  It's not a space issue: there is a more empty space below
each number as then the size of the numbers.

What is the mechanism that controls the size of these calendar fonts?
Is there a way to make them bigger?

Thanks for any suggestions.