DCC can not write to drive parameter p320 Motor

DCC can not write to drive parameter p320 Motor-Bemessungsmagnetisierungsstrom

The p320 is not offered in the list when "Verschaltung zu Operand" is selected from a real output. The list starts with p480, no smaller numbers.
From Starter Expert List, I can write during runtime to p320.
What am I doing wrong?

Background: In case of low torque output in torque controlled mode, the torque output jumps between 0.5 Nm and 0.9 Nm on a 1PH8 that is rated 39Nm.
If I reduce the IMag from 18A to 2A, the torque output in low region is ok.
I wanted to do an adaptive IMag inside DCC.

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Split from DCC interconnection with SINAMICS parameters: r21001 does not show up.