Inverse rates calculated on journal creation UI instead of deriving from GL Daily Rates table

We have imported inverse rates in GL Daily Rates table and it is restricted to 5 decimals. When user creates a transaction or journal, system is calculating the inverse rate as 1 / Rate instead of deriving the inverse rate from GL Daily Rates table. This causes a decimal difference between the table and calculated rate. 

Please guide on:

1. How can inverse rates in the transaction or journal creation page be derived from the GL Daily Rate table instead of calculating it? (Navigation steps will be helpful)

2. Where is the inverse rate which is stored in the GL Daily Rate table used in Oracle?