Item Category - Data Element and Domain - PSTYP (internal display )vs EPSTP (external display)

Hello,

Was hoping I could get some insight on the data elements of PSTYP and EPSTP... Let me explain what I'm trying to do...

I want to explain to a developer to append the "item category" data element on a custom table we have and allow it to have a drop down (domain) of the values of the Item category in purchasing document (external display). This is the same values in EKPO where you can select a U (stock transfer) L (subcontracting) etc... The reason for this is I want this value to be passed to the PO Create BAPI during a custom process we have which creates these POs.

When I check the data elements in hte system, PSTYP has a value table of T163, which has a drop down of the item category values... However, the values (PSTYP) are listed "internal" meaning Stock Tranfser is to a 7 value (check table EKPO - PSTYP for example) instead of the external display, which is = U. It looks like data element EPSTP is the element which is contains the external values I want, BUT I do not see a value table assigned to this data element.

Is there a standard element and domain of these external display values , or do I just need to have them create a new data element and domain for these values?