Both of my frames are older and have semi-horizontal dropouts, so I have some flexibility.
Since the math is modulo 4, there are four positions corresponding to remainders of 0, 1, 2 and 3. I’m running 42/16 so that would be 58 mod 4, or 2.
My Schwinn can run that in two places on the dropout and I use the one that is further back to give my Superbe sidepulls a better chance to work on a frame that was intended for 27” wheels, not 700C.
My RockHopper has a rear U-brake, so I have to consider how the four positions work with brake pad clearance. I know I can run with remainder 1, 2 or 3, but remainder 0 is either too far forward and not properly in the dropout or too far back and would cause brake pads to hit the tire.
Otto