Fine. Everything seems to work.
Thank you for your quick reply and for confirmation.
There is only one caveat:
I don't have projects that use projections like Gauß-Krüger or UTM. That's why I don't need such reduction/correction terms during my work. In short, I'm not an expert in this area and, of course, it is not an adjustment problem.
On the one hand, the distance reduction is very important even if the network is of small extent, on the other hand, the direction reduction is only useful, if the network extent is quite large - as far as I know. So, most adjustment applications supports the distance reduction but not the direction reduction.