Exchange rate when posting Advance in foreign currency

Dear Experts,

We are facing an issue with posing Advance in foreing currency. We have a business requirement to post document in FI in transaction currency (i.e. advances / receipts in foreign currency must be posted in foreign currency, and advances / receipts in trip currency must be posted in trip currency).

For doing so we set in img activty "Define Global Settings" the "Choose foreign currency per Receipt" option in frame "Settlement of Foreign Currency Receipts".

Employees are posting advances/receipts in appropriate currency and the currency is modifed in PR05 before settlement/transfer to FI.

So far so good...

Problem is : When modifying the settelment currency to the foreing currency in PR05 any modified exchange rate is lost. The FI document is posted and the amount in internal currency doesnt match the original amount in trip currency anymore (but using an amount at date - trip date or posting date...).

How can we manage to post in foreign currency while keeping the modified exchange rate for internal/company currency ?

Thanks by advance !

Of course any helpfull answer will be rewarded 😊

Mathieu