Purchase requisition to Purchase order conversion

MRP generated the stock transport purchase requisition. (between two company codes)

When i converting the PR to PO, system creating Stock transport purchase order, item category as "U" instead of Standard Purchase order, doc type: NB.

We are using STO between two company codes, PO Doc type should be "NB",Delivery type" NLCC and Checking rule: B - SD Delivery.

Please give suggestion, where i'm missing the configuration.

Thanks

SUNIL