Security Hierarchy when using Position Hierarchy

We're using position hierarchy and we have document types set to Purchasing.  We want to allow view only access to purchase orders to non-buyers, and people not in the position approval hierarchy.  We've created the new job, position, changed the document type to hierarchy/full, and configured the security hierarchy in the purchasing options but the users are still not able to query the purchase order info in the purchase order summary form.  Any ideas what we're missing