Freight Charges @ delivered quantity instead of sales order quantity

Dear Friends I want to apply and calculate freight charges @ delivered quantity instead of sales order quantity. For Example; Sales Order was of 10 MT whereas Quantity delivered was of 12 MT or 8 MT. I want to calculate Freight on 12 or 8 MT, as the case may be. I am using R12. Please help me with mentioning targeted options. Thanks and Regards

Not very sure but I think can

Not very sure but I think can be done using freight cost and modifier.