Different Values are populating as CURRENCY_CD_BASE in PS_REQ_LN_DISTRIB

We've a specific scenario where an Australian Business Unit(AUD) is raising a  Requisition in Indian Currency(INR) and it should be distributed to Indian Business Unit(INR) but what we are noticing is depending on the selection of Override/Default we are getting different values(sometime AUD and sometimes INR) in the CURRENCY_CD_BASE in PS_REQ_LN_DISTRIB. We want to understand how it works and what should be correct value stored as CURRENCY_CD_BASE in this scenario.