Thanks for the replies 
I’m not at all surprised if a big part of overall sales occur during the launch week. There are so many factors in favor of that period (temporary price reduction + extra visibility as the newest release + maximum amount of potential players who never tried it yet).
One more thing though: assuming it is monthly (if there is something to send), is it always at some specific time in the month? Like let’s say royalties from March paid at the end of April?