Maybe if the player had to fall for a little bit of stage after the tutorial section, and then be prevented from completing it until they passed a threshold, that would have communicated more quickly what the intent was. As it was, I didn't realize it until midway through the second level; I basically blind-lucked my way through the first stage. :P
Agreed, having some narrative elements might have helped explain it. I'm still thinking, from a game perspective, knowing the target number (or some threshold) would be useful. Otherwise, I'm just trying to hit 18-20 as much as I can. (Though that might be your intent, which I would respect.)