it is the INNER groove, or the one FARTHEST from the plug...there is a "stopper" on the sensor that prevents you from pushing it in any farther i.e. far enough to use the OUTER groove
No bfg drag raidals with zero boost,just had the trans put in by my self and did not want to have to tow it home from the track still allot more in this car with some traction.
Ed