sorry my mistake. The custo in split valuation is used to release a standard cost estimate at the valuation type level.
For your case, the value of the RM is take from the header segment of the material master. So your header RM must be set as S price control, right?
If you want the system to use the valuation type segment, you will need to use procurement alternative, where you can create a proc. alternative for each valuation type you want to use in your costing.
hope that helps.