Big chunky limit switches do not not necessarily give you good positioning, they are more concerned with reliability than a fine switching tolerance.

The best positioning switch is probably an opto slot with a built in Schmitt trigger. But if the switching point chances to align with a completed step you can still go +- one step.

Perfection is probably a side paddle arm on the screw that winds into an opto slot. That would allow you to adjust the switching point to mid step.
I'm going to give it a go, but that's only because I am totally anal