Payables: Decimal issues when accounting foreign currency invoice

We need to understand what the accounting entries for a foreign currency invoice look like. Since we identified that if an invoice was created in a foreign currency (USD) with an exchange rate of 20.6358, when creating the invoice accounting, the accounting entries consider a different exchange rate to show the entry in the functional currency (MXN), we don't understand why the accounting entries consider a different exchange rate.

We need to understand the calculation to obtain accounting entries in the functional currency (MXN). Can you help us?