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Higher compression ratio does not directly impact Volumetric Efficiency of the engine. It helps thermal efficiency, and a higher expansion ratio helps deliver higher pressures on the combustion stroke.
In simple terms, think of a turbo. A turbo compressing air heats it up. Adding an intercooler can increase air density as well as prevent detonation. With the compression ratio of the engine you are doing the same thing, compressing air. Except inside the engine you have no simple way of decreasing the temps. Therefore, the tendency to detonate is higher. Its all just about pressures and temperatures.
Lower compression engine= lower peak pressures and less heat in the cylinders. But with a proper high compression engine you can still use a lot of boost if proper fuels, tuning, and temps are controlled. You just don't want to see detonation, and detonation is more easily prevented by reducing the compression ratio to give a larger margin of error.
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