Standard Orders vs Custom Releases for a GBPA.

Hi All, We have a scenario where standard orders are getting created from G-BPA where as we have custom release creation process and standard orders should not be created. During our analysis we found that Requisition Import program populates the suggested_buyer_id, document_type_code etc and enables the creation of standard order through seeded process. There are no sourcing rules defined for the item in question. My question is how the requisition import process populates these fields as it is very random and only few org it creates the standard orders. Any help on this is greatly appreciated.