Logically I would assume if you are going for 15 reps in the set, 10-11 the first attempt, 2-3 the second and 1-2 the 3rd attempt.
On the 20 rep set, 14-15 first attempt, 2-4 second, 1-2 3rd.
I could be wrong on the above though, but logically that is what and how I would think it would go...