Is this the expected behavior, If the invoice has been created, then the system don't create any authorization request for increased price amount.
System is expected to create a charge request without an authorization if there is a invoice in the system that needs to be charged.
This feature was provided to avoid delays in settlement, and also to support authorization-and-settlement in one transaction, which many
payment gateways support.
If the gateway does not support the same then please do System perform authorization and settlement in the collection credit card user exit call.
Then you can set the Authorization id in the case where it is void in the return values of the user exit.