Text fits into elements only for prologues=3

[Reissner]

I have a mp file

F3_01texUsagePlain.mp.txt

to be more precise the according mp file (github does not allow to upload)
which i would like to compile with

mpost -interaction=nonstopmode -recorder -s prologues=2 -s 'outputtemplate="F3_01texUsagePlain.mps"' F3_01texUsagePlain.mp

F3_01texUsagePlain3.pdf
F3_01texUsagePlain2.pdf

But then, the texts don't fit into the boxes at least if previewed in okular.
What I see is exactly what you can see after converting with epstopdf into the two PDF files.

This changes if I use option -s prologues=3 which also changes the font.
As you know prologues=3 leads to huge headers in the MPS file.

I observe also that the font style changes.
I would like to understand what happens and I would like to fit the texts into the boxes without prologues=3.