I ran it in 2015 so rules could have easily changed since then. But from what I'm seeing in the rules, they allow for this exact scoring system.
III. Format Details
1. Qualifying Rounds
Players will complete 2 rounds of 9 Pin-Holes during Qualifying. Each Pin-Hole will consist of a pinball machine with a target score. The number of balls it takes for the player to reach that target score will represent the number of Pin-Strokes earned for that hole. Should a player not reach the target score after a full game is completed, a stroke value will be determined based on how close the player was to the target score at the end of their game.
For example, the target score of CSI may be set at 10 million points. A player will continue playing the game until he reaches 10 million points. If reached, the number of balls it took to reach that score will be recorded for that Pin-Hole. If the player fails to reach the target score after 5 balls are played, they will be awarded a score based on how close they were to that target:
8,000,000 – 9,999,990 points = 6 strokes [80% of par]
6,000,000 – 7,999,990 points = 7 strokes [60% of par]
4,000,000 – 5,999,990 points = 8 strokes [40% of par]
2,000,000 – 3,999,990 points = 9 strokes [20% of par]
0 – 1,999,990 points = 10 strokes [<20% of par]
A maximum of 10 Pin-Strokes per Pin-Hole will be enforced. Scores will be cumulative across all rounds played.