Down ward PO Revision does not initiate Approval of the PO as per PO Approval Hierarchy

 Dear All,

When we make change in Approved PO to increase Either unit price or quantity system initiate PO Approval Hierarchy.

But However, if Unit Price or quantity is reduced system does not initiate PO Approval Hierarchy and allows Change maker to approve it from his side.

Is there any set up which would make PO going for approval for any single changes made in Approved PO??

Waiting for the prompt actions

Thanks 

Abbas