David Vizard in his book "How to Build Horsepower" give a general, non-mathematical, description of the ignition process vs rpm.

So I don't violate copyright, I will paraphrase.
He writes that apart from the physical characteristics of the combustion chamber, RPM, manifold vacuum, fuel type, and other factors; mixture motion has a big effect on the combustion process.
Best power output occurs when the cylinder pressure reaches its highest level at about 15 degrees after TDC under all conditions. This is governed by the geometry and mechanics of the engine.
When the engine is turning below ~2000 RPM, the combustion rate of the fuel/air mixture is about the same. So, as the engine speeds up, the piston is moving faster, but the combustion front isn't, so it will take about he same amount of time for the combustion to finish. This means that the ignition timing needs to advance as the engine is going faster to have the same time for combustion before the piston reaches 15 ATC.

Between about 2000 and 3000 RPM, the mixture is moving fast enough that it starts to increase the rate of the fuel burning. The faster the mixing, the faster the fuel burns. After about 3000, or so, the rate at of mixing is increasing the rate of fuel burning very closely to directly proportionally to the increase in RPM. Therefore, no change in timing is needed as RPM increases.

This is all generally true for a 4 stroke internal combustion, normally aspirated engine. But each engine and setup will vary the details.

I highly recommend any and all books by David Vizard. He has decades of extensive experience as a race engine engineer and writes in a very clear way and backs his statements up with hard data and clear plots.
The "How to build Horsepower" book is particularly good.

Robert