[rookie]

With faster air speed you have less localized heat, this is why a tighter quench area will allow more compression before you encounter detonation.

As the mixture improves and burn speeds up then you ignite it later, so now your burn is concentrated on pushing the piston down the bore instead of being compressed.

What I wonder is at a higher rpm you now don't have time to burn the whole mixture unless you progressively lean it down some or add some timing back in.