Production Order Splitting Issues

We have Order Based costing and not using PCC and ML

Say I have created order for qty 100 after two or three operations we can find few pieces are inferior quality so I would like to split the order, when i split the order by qty 90 and qty 10, the parent order is calculating the Mtrl cost + operational cost but child card is only showing Mtrl cost from material master

The Cost suppose to be Rs 1000 for Qty 100

Desired output Parent order – Rs 900 (for 90Qty)

                                Child order – Rs 100 (for 10Qty)

But I am not getting the cost proportionately for Parent and child order, by product picking the cost/rate from material master.

Please help me it’s very urgent and crucial.