Multiple Work Definitions with the same Byproduct

Here's my scenario, Cost method is standard cost. Work method is Process Manufacturing.

I have item A that is a by-product output for several work definitions.

Item A doesn't have a work definition where item A is the primary product.

My question…

If item A isn't a primary product on a work definition then how does cost rollup calculate the cost for item A?

• Is item A's rolled up cost calculated as an average of all work definitions where item A is a by-product output?
• Does the cost rollup process prioritize a work definition to use for the cost rollup?