The black plastic magnetic collar that slides over the distributor shaft, needs to be flat/flush with the pertronix module. In other words, when installed, the top of the plastic collar and and the top of the module are supposed to be at the same height.
Usually, if there is a mismatch in the height, it is the top of the plastic magnet collar being a little shorter than the top of the module because of slop or wear in the distributor shaft.
Pertronix' fix/recommendation has been to install an appropriate thickness washer or o-ring underneath the black plastic magnet collar to correct any difference in height.
