If You look at the arch - you can calculate or measure the length of the arch-bow. You also know the measure of the bricks + the normal intendt join and then you can divide the archlength through the (bricks + the join) and you get of course not an integer but you get a floating-point - number.
If you now divide the archlengt through the next bigger integer, you will now get slightely bigger joints or smaller joints by using the next smaller integer.
made a gdl for this some years ago:
https://bimcomponents.com/GSM/Details/14716
(Attention: download - just draw the downloadbutton ino Archicad.)
its german but you can get the ides:
AC5.5-AC27EduAut, PC-Win10, MacbookAirM1, MacbookM1Max, Win-I7+Nvidia