Derivation of Transaction Type

Hi all

in some of the postings our SAP HCM interface should deliver the transaction type. But as SAP HCM does not know the transaction type (TRTYP) I would like to use the table V_T856K (transaction OBMA) for the derivation. How can I activate this derivation? Are there specific entries for the tables TRWPR, TRWCI and TRWCA?

Or is there another way of filling 'RMVCT' in postings with their origin in SAP HCM?

Or is there a possibility of enabling this field within the substitution (transaction OBBH)?

Thanks for feedback!

Julia