Why is Operation Yield not considered on rolled up Cost?

We want to factor the yield on the standard cost of assemblies that have a high failure rate. We populated the Yield and made sure that the Include in Rollup is checked on the Operation Yield tab for the Routing of Item K8610. We then submitted Supply Chain Cost Rollup - Print Report. The Yield was not included on the Cost Rollup. Note that we are on R12.1.3