Yahoo62278's campaign requires a minimum of 25 posts per week. The 1 Merit requirement is very low, if you can't earn 0.04 Merit per post, you should indeed not be paid for it.
I'd make it some sort of running average though. Maybe 5 or 10 merits over the last 4 weeks. There is a lot of variance in how merits are sent and I can imagine an otherwise decent user falling short of it in one unfortunate week.
For example I earned 10 or so merits on my last 20 posts, so that
seems like 0.5 merit per post but only 3 of those 20 posts got merited. I'm quite sure I've had streaks of 25+ posts without merits.