Do you mean limit on the client side or on the server side?
I think that hard coding this limit onto the client side is a bit of an iffy solution, incase of future events where we may want screenshots of all CAs; and adding a config option kinda just further complicates setup for players.
Ideally they wouldn't think they need to change anything in the plugin config as that's how I've stated it works in a few dif places.
We could certainly look at making groups have the ability to decide whether they only want new tier achievements to he sent, in which case the solution would be very easy -- determine points earned, and then see if the player's current points minus earned points puts them at the previous tier.
I'm definitely open to the idea just not sure if coding it into the plugin side of things would be the best way to do it