Out of curiosity, this evening when I tested my chlorine level (I always use a 10 ml sample), I did it twice; the first time using my usual 2 scoops, the second time using 1 scoop. Oddly, I got slightly different results; 2 scoops FC = 4.5, 1 scoop FC = 5 (samples were taken from same location in the pool).

Anyway, like you said, it's apparent I can use 1 scoop instead of 2 so I can get many more tests out of the same DPD powder bottle.