The coil must be held off the magnet track by ~1mm (.035 -.039-inch) through the use of mechanical or air bearings. Note there is a high attraction for between the ironcore coil and magnet track.
The Ripped series positioners are set at .035-inch when warm and energized. The gap can change about .010" or so when energized, plus a slight change when coil and bracket are warm from operation. Note that the flatness of the epoxied bottom of the coil tolerance is +.013 / -.005. Thus this gap should be checked on both ends of the coil and checked when energized.