I could find similar issues here and here.
I also found some interesting intel about the ImageableArea notion in this post and at the section “10.4.7.1.2 Changing the printer margin settings” of this documentation.
Looking at my ppd, I can see this:
...
*PaperDimension A4/A4 210x297: "595.440002441406 841.679992675781"
...
*ImageableArea A4/A4 210x297: "8.39999961853 8.39999961853 587.039978027344 805.679992675781"
...
This means that the bottom, right and left margins are 8.4 pts, while the top margin is 36 pts wide. That should explain why I cannot see the upper parts of my prints.
Let’s try with a top margin of 8.4. That would mean that we put the following value:
return 841.679992675781 - 8.39999961853
833.279993057251
And therefore change the ImageableArea line to this one:
*ImageableArea A4/A4 210x297: "8.39999961853 8.39999961853 587.039978027344 833.2800003814699"
Now, my printer doesn’t cut the top part anymore!