It is like STO procedure with Excise & Taxes carrying from PO to STO Invoice.
STO can be two types-With MM Procedures & SD procedures.
If we follow SD cycle(PO>>DEL>>Proforma Invoice>>Excise Invoice)- here system will pick the pricing form your OVKK & STO Customer sales area settings.
(this STO customer we will assign in STO settings of IMG)
Here in last step you want what kind of Invoice matters-Pl let us know on this.
Also are you following the above cycle & If not let us know your current STO cycle..
Phanikumar