What is the usual AME approval escalation when a GL distribution is modified on a Purchase Order?

We are using AME to direct our approvals.   A buyer with a $200,000 spend limit created and approved a PO for $250,000.  The PO escalated to her boss who then approved it.   The approval was final - no further escalation needed due to the boss's spend limit of $300,000.

The buyer then changed the GL distribution which did not create a revision but did change the PO to require re-approval.   She re-approved but the PO did not escalate back to the boss for approval.   

Question:   To my knowledge, there are no custom settings for approvals.in setup, etc .   Having said that,  is this 'normal' AME  or Purchasing behavior to not require escalated approval in this situation?