Services Procurement Question

If anyone has experience with this please let me know.  We are implementing Services Procurement, iProcurement, OTL and iExpense.

This scenario involves contingent workers;

CWK is on-boarded with a PO and the assignment is made via Manager Self Service. Note, there is no field on the assignment where a default expense account can be entered.

Create Time card is fine, it reads off the PO and all is well.

My issue is, that iExpense and iProcurement have no default expense account reference.  We thought since the PO was attached to the HR record, the default exp account would come from the PO line, but no such luck.