A z-index of 9999 is not a layout decision, it is a symptom of a stacking context that is not understood. The next component needs 10000 and the page becomes unmaintainable.
Impact is importance multiplied by the confidence tier’s weight — SPECIFICATION 1.0, RESEARCH 0.7, EMERGING 0.3, EXPERIMENTAL 0.1. Two rules backed by the same class of evidence therefore always carry the same weight, which is what makes the score reproducible rather than hand-tuned.