Sales order derivation on profitability segment from WBS element

I have an issue where we are creating a contract in CRM. The contract then ties to a project in PS and then has a WBS element assigned to it. In looking at the settlement rule and the profitability segment the sales order/contract is not being populated. We looked into having user exit COPA0001 populate it for us, but sales order can not be a target field.

My question is, shouldn't the sales order derive automatically already? If not, any ideas on how to get it populated in order to flow to COPA?

BTW, we are on CRM 7 and ECC 6.0.