I'm probably blind, but I've looked everywhere in the backoffice area, in the _main.php, and also searched for a while in the forum, but I can' find where to set the archiving method, monthly, weekly, daily or by number of posts. I guess ALL posts are actually archived the same way and it's a question about how many posts to display when calling a blog...

Sure I could go deeper in the code to find it, but I don't think it's a good idea to change things there, that will probably give me problems when it's time to upgrade. And anyway, I can't imagine that it's a hardcoded thing, right?