Min confidence parameter can be treated as a probability filter of true positive matches (default 0.2, meaning that Emy will not return matches that have lower than 20% probability of being true positives).
Useful for most users as it takes into account all possible query cases: query is longer that the track, track is longer than the query, query contains multiple tracks, query contains track snippet and some other data.

Minimum track or query coverage used to provide additional filter of false positives (default = 0.0, i.e., specifying 0.2 means at least 20% of track or query length has to be covered for the match to be returned).
Min coverage provides stricter filter guarantees comparing to minConfidence, and is useful in cases when you know for sure that the query stream contains only a subset of track and no other data.
There is no reason to use both minConfidence and minCoverage filter parameters with the same value, as minCoverage will always act stricter than minConfidence.