Form with UI customization - How to check if UDF is moved or still on UDF Form

Our customer has positioned many UDFs in the main Forms of the item master, using SAP UI customization.

Now calculations should be made in the UDF and written back.

Is there a way to check whether the UDF is on the UDF form or the main form when writing, in order to address the right field and avoid an error Message?

Thanks for your ideas in advance.

Regards

Jürgen Zimmermann