POs are auto approved and dispatched to vendors without higher level approval

 Below current setup is allowing our buyers to  bye-pass higher level PO approval and dispatching to vendors without PO amount approal.

User A ( buyer as well as PO higher level approver )

user B (  buyer Authorized to create PO for buyer A )

Our issue : Buyer B is able to source approved requistions into PO  with A as buyer. Since the buyer A has higer level approval, the PO amount approval AE program is auto approving the PO and dispatching to vendor site. The expectation is, the PO should be routed to buyer A's work list.

Question : How can I prevent the auto approval for buyer A ?  where can I look for the configuration to turn off the PO self approval for buyer A ?