You want it to float freely at the center of its field but if there is play, shim it toward the sensor as long as it doesn't push it from floating. Will just put stress on bearings that they arent designed to handle.
It seems the sensor boards themselves are a big variable with no two being the same though. So a specific sensor clearance prob doesbt matter a lot if you have a 5+ degree variance. We have seen some new motors come with as much as 10 degrees off on one sensor lol.