Outgoing SD Excise Invoice ( Foreign Exchange Type Determination)

Hi Sapients,

Pls clarify my query below,

While creating Excise Invoice with reference to SD Export Billing document,

the Currency conversion rate is determined by the Exchange Rate type "C" in OB08. But i am unable to understand how the System takes "C" into account while creating Excise invoice among all other Exchange Rate Types.

Example:- When I am creating a SD invoice Exchange Rate type M is determined.