Auto Reject if Order is higher than the requisition line - Change Currency scenario

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Dear All

We have a requirement that Purchase order should not be higher than the Requisition amount , to full fill the requirement I make the rule as auto reject If Amount Exceeded Percent is higher than 0 in requisition level , which is working fine , but there is an issue , in case if user submitting requisition of 100 SAUDI RIYAL and Buyer changes the currency to USD , still the Purchase order will not get rejected less than 100 ,even though the equivalent USD is only 27.00 USD , is there is any way that the system look