advance pricing Reprice

When a sales order has an order level price line entered at the time of order entry, the Advanced Pricing functionality of the R42750 adds the line to the order

When the order is shipped and some of the lines are back ordered or cancelled, the R42750 needs to run again to update the order level price line When a back order occurs, the order level price line is recalculated (by R42750) but it does not pro-rate the amount based on what has shipped and what is remaining ? do you why, what is the standard process to pro-rate the amount based on what has shipped and what is remaining?