Unit Cost for Margin Calculation is from Inventory module instead of Cost Management module

Hi

We use Periodic Average Costing; we have a average cost calculated in Inventory module, then we have another cost in Cost Management module which includes the additional charges such as freight etc.

Therefore the cost in Cost Management module is  more accurate as it includes charges such as freight , duty etc , whereas Inventory cost is just the Item Cost (unit cost)without additional charges such as duty,freight,insurance ...

Now in Order Management module the Margin is calculated using the unit cost in Inventory module, therefore margin calculation  is not accurate.

Why Oracle does not pick up the item cost from Cost Manager , instead it picks it up from Inventory module?