There are two processes that can log debugging info -- the ISCAgent process itself and the cuxagent processes the ISCAgent starts -- the cuxagent processes are the ones that interact with the instance.

The messages in /var/log/messages are messages logged by the ISCAgent.

When you enable debugging by adding the line:

mirroring.console_logging_enabled=true

to the conf file, you are enabling debugging of the cuxagent processes the ISCAgent starts.

The cuxagent debugging is logged to the iscagent_console.log.