Contract Manufacturing demand prioritization

When we have mutiple contract manufacturing sites able to produce component item for an assmebly item.

We noticed that demand priotization of the assembly item is not happening as per demand date accross the contract manufacturing sites. How is this controlled or how is demand prioritzation happening

In the below scenario SKU3 is consuming raw material from both CM1 and CM2 how is the demand priotization happening in this scenario. In our runs we see the demand prioritzation is very erratic. Its meeting forecast which later compared to sales order demand which is earlier.