Plug gap

There seems to be some diminishing returns with widening plug gaps. Peak HP is one thing, but again when an engine is at peak power/load/torque you’re going to be around peak demand for your ignition.

If your ignition can’t supply the output, it can’t keep supplying the needed spark at peak. A bit like the duty cycle of a welder. Spark may be good at idle, but run out of steam at peak demand.