Quoted from Snailman:
I believe this is incorrect. I think the # of balls in WCWS is based on the # of modes in the ladder you just completed. Each time I've completed the left scoop ladder, my WCWS was only 2 balls (to start off, prior to any add a ball). And when I completed the right orbit ladder, it was 4 balls for WCWS. I'm pretty sure about this, but not 100%.
I think it's a good nuance -- the WCWS for completing the right orbit ladder is MUCH harder than the 2 modes on the L scoop.
I've only completed the right ladder, but it's a great mode and a cool surprise.