I'm not sure there's a firm pattern, but my impression has been that the fen posts about specific plot issues or character events elicit more discussion than those that raise a number of things at once. There may not have been enough of the latter to really judge that.

I also think that people have peaks and valleys in the amount of free time they have: sometimes that means I've gotten way behind on the game and can't post to alt_fen because of it; other times I'm keeping up with the game but don't have enough time left to post here; other times I just don't have an idea about the topic that's being discussed (like Amycus -- he's beyond me a lot of the time).

Not sure. Don't get discouraged, though!