easyJet A-319s config is 156y. A load form is completed prior to boarding with the breakdown of the expected pax and actual bag weights used for the bags checked in. There is a guide issued by easyJet for the Dispatcher to determine where to load the bags for an acceptable trim.
This information is fed into a rugged laptop by the Flight crew into their weight & balance system. They would use an even pax bay split for the fuller flights. However, if the pax load is below 100 ( I believe ) then the cabin crew will indeed count the actual pax bay split during the headcount and the actual pax bay split will be entered to give the final figures prior to departure.