Sorry bohm on two counts. Firstly by "waste of time", what I really mean is that I don't there is really a way of correlating the convention baptism ratio to overall ratios with any science. I think it's simpler just to wait for the yearly report as that has the figures. I didn't mean to pour such scorn on your efforts :-)
Secondly, I thought it was peaks between years you're right - for increase it is averages.
I think most of the baptisms are at CAs.