User to position reconciliation in IDM

Dear Experts

After working with IDM for a while I still cannot find an obvious way to reconcile non-HCM users with their positions. For example, users already exist in the ABAP client and are not assigned to positions. Then IDM with HCM integration is implemented and new user creation is driven from HCM to IDM. If a user ID already exists for a user I can assign the user Id to the position via the 105 record. However IDM doesn't seem to know that the user ID now has a position and doesn't populate the User record in IDM with the HCM details. Am I missing something here?

Thanks

Barry