There are two sets of scores that they’re talking about.
During the ride, they’ll say, 6, 7, 8, 9 etc. In this case the high score is better, just like regular dressage. They’ve given out some 9’s and I seem to recall Lucinda Fredricks, the leader, got a 10.
Once the ride is completed, there’s a formula to take the percentage (say 75% in the case of a very good ride, 55% in the case of a poor ride) and convert it to penalty points. At this point, the low score is better. In the 30’s and you’re in the hunt. David O’Connor laid down a 29 at the Sydney games with Custom Made, which I think is the only time someone beat 30.
Note that the USEA score conversions are very simple, just the inverse of the percentage: ie 70% -> 30 penalties. The FEI tests use a different formula that I don’t recall at the moment.