Check Duplicate PO No. By Sales Document Type with irrespective of customer

Dear Team,

Requirement: PO No. shouldn't repeat in the particular Sales document type.

Currently :

1. I have set the configuration in VOV8, Check po no.--A

2.and set the warning to error by using T-code OVAH (E)

This setting satisfy only ---PO no. is check's by customer wise in that particular sales document type..(not for other customer)

I mean if i use the same PO No. with other customer in same sales document type it is accepting(it is not giving error message)

so I need here to check PO no. by sales document type irrespective of customer nos.

So please guide me regarding this

Thanks

YRH SP