ReSA Total for Returns

I need immediate assistance to create a ReSA TOTAL for returns.

There is no extension (unit retail * QTY) in SA_TRAN_ITEM for me to total based on ITEM_STATUS (R).

And if I use VALUE from SA_TRAN_HEAD where TRAN_TYPE = RETURN, my total gives me some ridiculous number. There also can be issue for transaction where there is a sale and return on same transaction. 

Can someone please share there experience or best practice to totals returns for OMS? Also can someone share how can I show totals with inverse sign, in roll up e.g. negative field can be rolled up as positive total?