Covered code MSI is the number that means something

Three mutation metrics are reported and two of them mostly restate line coverage.

MSI                     over ALL mutants, including the
                        ones no test reaches. this is
                        coverage wearing a costume.

Mutation Code Coverage  the share of mutants any test
                        reaches. also coverage.

Covered Code MSI        of the mutants tests DO reach,
                        how many are killed. ← this one.

85% covered MSI against 94% line coverage is the gap.

Setting a threshold on covered MSI and none on the others is what stops the metric being gamed by writing tests that execute code without asserting on it — which is the exact behaviour a coverage target encourages. The gap between line coverage and covered MSI is a useful single number to track: a large one means the tests run the code and do not check it.