Hi Crabman.
You are on the right track.
What you have to understand here, is that the concepts which others have discussed (flame front speeds, timing and better burning) relate to design parameters of a particular engine using the Otto cycle - not the theoretical thermodynamics of the engine.
Oggers and CW say that faster “flame front speeds” make engine X more efficient at higher compression. I say you can make engine X just as efficient by operating it at low RPM. In fact, this is what the world's most efficient piston engines do - they operate at extremely low RPM.
Oggers and CW say that “better burning” make engine Y more efficient. If this were true, consider what would happen if you increased the compression ratio of an engine at constant fuel flow. Oggers and CW say that you will more completely combust much more of the fuel. This should mean that the exhaust gas temperature should increase. We saw from the linked document in post 41 that in fact, completely the opposite occurs – EGT reduces. Ask them to explain why “better burning” (which obviously they are implying means less unburnt fuel being wasted) causes the EGT to reduce.
You can easisly take their piston engine arguments out of the equation by running a large diesel engine at extremely low RPM (where flame front speeds mean jack sh*t and where the fuel is essentially completely combusted). But why does compression ratio still affect the thermodynamic efficiency?
I can tell you why - because you are adding less energy to the fluid.
As for the practicalities in a car or aircraft of a large, extremely low RPM diesel - I obviously understand this and a multitude of other reasons why for practical purposes there other considerations in making piston engines adaptable and useable over a large range for a particular application. But these are inconsequential to the FUNDAMENTAL concept of the OP.
Not only will Oggers and CWs arguments not apply to a large, efficiently designed and operated piston engine, they also fail to apply to a turbine. This is why they have both failed to answer my question about this so many times – because their reasoning simply can't explain it.