Apologies in advance, I may not have caught the gist.
But I think a calculated field may give you more control.
ELSE "Not Proficient"
and put that alone on the color shelf.
I'm not sure that I quite understood the Average,
but I instead used SUM([Results]) and added a
quick table calculation of Percent of Total,
table calc settings shown below.
Please see workbook v18.1 attached in the Forum Thread.
285139calc.twbx 2.6 MB
That did the trick. Thanks a bunch.