It's best if sources try to exhaust their source allocations, even if it means giving posts higher amounts than is typical. If you have 150 source merit and you only see 3 merit-worthy posts in a month, then I'd rather you over-give each of them 50 merit than let the merit expire.
I can't say I completely agree with theymos here, but I get the reasoning behind it. If all Merit sources would do this, the amount of Merit created each month would be equivalent to the total of all Merit sources.
I was overflowing with sMerit - over 1,000. I decided to trust Theymos and do what he suggested. He removed me as a source. :/
Merit is centralized and political - if Theymos likes you; it's hard to suggest otherwise.