There are different motor drivers on the boards. You may notice some strobong variences at fast speeds between the versions.
Mirror getting off it a completely different thing. Try this:
Watch the mirror home & note which direction it moves & knocks against the standoff. Put all the address & personality switches on. This puts the fixture into set up mode. Move the mirror by hand and you will feel the motor steps. Then move it to hit the standoff as if it were homing. When it hits the standoff the mirror should rest on the standoff on a complete motor step. If it is between motor steps you need to back the mirror off of the stand off, loosen the set screw that hold the mirror onto the motor, move the mirror to the stand off (you should not feel the motor steps), tighten the set screw & check to see if the mirror lands on the standoff on a complete motor step. If not try it again. It may take a few times to get right. Once you get set test the fixture.