Exclude negative balances from credit check rule

We are using Credit Management 12.2.5 and are having problems with negative "past due" receivables balances (credit memos, overapplications, etc) putting orders on credit check failure hold. We only want to consider positive past due transactions and credit limit failures. How should we change our rule to accomplish this?  Thank you.

Our credit check rule is set up as follows:

Credit Check Level:  Sales Order

Credit Hold Level:  Sales Order

Use Pre-Calculated Exposure

Include Open Receivables Balance (we want to consider only positive values)

Include Payments at Risk

Include Uninvoiced Orders

Include Orders Currently on Hold

Include Returns

Maximum Days Past Due   60