Hi
For BOM material please tell me is it main item? I mean are you looking for VPRS of main item or sub item or do you want cost of sub items transferred to main item? If possible please paste the screenshot of condition tab analysis screen of VPRS condition. It will help us to understand the issue.
If you want to transfer cost of sub items to main item then you can do this in copy control from delivery to billing at item level. There is an option which you can see there.
Thank$