Why invoice was validated without requiring PO receiving, though PO is 3 Way match

Summary:

Hi,

While performing testing for invoice approval rules, we found that some 3 Way PO based invoiced are behaving differently than others when it comes to Invoice Validation. PFA example where a PO is created for supplier X and line type is 'Order by Amount'. Its invoice did not had any hold and passed the validation directly without needing any po receipts whereas when we create PO for supplier Y which does not have any settings on its site level, its 3 Way match PO based invoices get receiving holds.

Can someone please have a look and let us know why / how this is happening?