At the moment, there is no easy way to determine which of the TMs in a TM group are actually contributing to translated content.
It would be really helpful to have an auto action in the workflow that generates a report indicating which TMs in a given project have actually been leveraged.
This would make it easier to find our whether TMs are actually giving you matches and, if not, remove them from the respective TM group. Vice versa, it would also make it easier to check whether adding certain TMs to a TM group will give you more matches.