There's a lot of hard science out there on flame kernel propagation. Say what you will, there's pretty good consensus at this point. It's part of the reason the big auto companies have been looking at newer ignition technologies lately, like jet and laser.
Here's another example specific to spark plug gap (picture below):
https://doi.org/10.1016/j.apenergy.2017.01.059
And check out the "Burn Rate & Ignition Advance" section from this (non-scientific, but easy-to-read) Grape Ape Racing white paper:
https://grapeaperacing.weebly.com/up...06275/heat.pdf
