Difficult to understand.
The mode matching does not change the recycling gain. It changes the coupling of the incident light into the cavity.
It changes the reflected and accumulated power, but the recycling gain is not affected.
The recycling gain is determined by the optical configuration and the optical loss in the cavity.
In the actual measurement, of course, we should take both of the loss and the mode matching into account.
But this is the issue of the measurement method.
The essential questions are:
How much is the actual recycling gain? And how does it affect the signal extraction?