The higher the resolution of the coupled axis, the more precisely they match while running code or jogging.
I tuned motor X to 40000 steps per, 100 ipm, 20 accel
B 30000 " " "
and they tracked within 0.0001 on the DRO's when stopped anywhere in a program run or while jogging at any speed.
Tuned to 2000 and 3000 steps per, or any other low resolution, they follow each other around 0.001 +/- due to the rounding I suppose.