Seemingly is is based upon total placings overall, and then you get one for each that you have finished all 20 based upon the aggregate of all those results.
Sorry not based on aggregate, but on the individual placing for that art, you will notice the first was a 75/75 while the second 78/78, though on the art itself it gives the overall results.
Someone else I saw got 80/80 despite having a win rate of 32/20, however I presume that for that faction and Combat level it was the highest
