This does not sound like a correct requirement to me. How can approver 3 with position c, be skipped for a higher value order for the same document type while being part of approval for a lower value order.
Please clarify with business.
The above requirement cannot be modeled in Position hierarchy.
In this case approver 2 is acting as dual role.
He remains as Manager and Secretary for PO approvals.
Pl Suggest anyway to achieve this.