When I said 2:1 I meant 1:2 motor:spindle. But you understood what I meant. I suppose it would work if the pulses were exactly 180 degrees apart on the encoder on the motor.
This is how I made my index sensor. The reason there are two sensors is one feeds the CNC control and the other feed a tach on my DRO that I had from before CNC.
I also made that slot a lot bigger by the time I finished it.