Approval Rule: Functional constraints of Currency based User-Defined Attributes

Summary:

I want to confirm the functional constraints of Currency based User-Defined Attributes, that we are facing problem now. Please provide your suggestion.

Content (required):

We have multiple BUs.

And one of the BUs in Philipine requires to use approval amound in Philippine Peso in the requisition approval rules even though the BU's functional currency is USD.

So, to fullfill this requirement we have created a currency based User-Defined Attributes, that convert "Requisition Approval Amount" to PHP(Philippine Peso).

And we have used the user-defined attribute in the approval rule for the BU, that rule have a condition "Requisition BU = the BU", too.