I have a rotary axis A and an optical homing switch. The A-axis motor is setup with low acceleration so it takes ~1 second to get up to full speed.
My problem is that when I use 80% homing speed and G28.1 A0.0 the machine runs well past the optical slit.
I'm guessing that it starts slowing down once it passes the mark but that is not really zeroing....
If I reduce the homing speed it is closer but it still makes me nervous knowing that homing position depends on homing speed....?
Am I doing something wrong?

If your accel is set that slow that it runs past the slot then what you will have to do is make the slot wide enough so that doesnt happen.
As you say however homing speed does affect things so if you ever change the homing speed again then it will be different. Also if your acel is really that slow then you will have to make sure that any time you home you are far enough away from the slot to allow the axis to get to full speed.
Hood