Majority of colleges do not use the subject tests for admission (except a number of those require them for home schooled students). Only a small number still actually require them from other than home-schooled students. A number that previously required them now either recommend them or say they will consider them if submitted.
The percentile ranking for subject test scores is not a relevant consideration for those colleges that require or recommend them. Only a minority of students take them and those are mostly your higher ranked students who will be attempting to apply to high ranked colleges that consider subject tests. That self-selection in taking the test is what results in the skewed percentiles, e.g., very often an 800 math is only in the 80 percentile range. The issue with subject tests is demonstration of proficiency in the subject and a high score does that