Dividing by 2 would only make sense if the piston stayed centered in the bore but it doesn't. The piston moves around in the bore as it travels up and down and with load changes.
.012 is too much piston to wall clearance. A forged piston needs more clearance than a hypereutectic piston does due to the greater heat expansion. Probe recommends .002 - .0075 for their forged SRS pistons depending on bore and application where as they recommend .001 - .0055 for their high silicon FPS pistons.
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