I dont know for sure.
But I think some of the reason to "side-gap" it is to shorten the side-electrode because then it is cooler, so less chance of pre ignition and detonation cause of an overheated side electrode tip. Especially in very high compression and engines that runs hard long. Like race engines usually do.
And at the sametime file it "round" on the edge since an spark like to spark of edges and not someting flat.
How much People cut the electrode is probably induvidually. but I think 1/3 over the center electrode is often used in normal engines.
People probably have differnet opinions though, but I think it is more of an safety issue than Power. And the plugs dont last as long either.
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