I guess since the SP is seated on top of the cylinder head for the in-line 6, the best method is to have the arc go across and not blocked by the prong. This design according to manufactures causes the prong to wear faster, so four is better than one, thus with a platium tip, the 100,000 miles spark plug.
Though, I would think it be better for less chance of misfiring too :dunno:
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