It's an interesting question. One would think that as long as the mounting is solid with no gaskets, that there will be some attenuation but not much. I like the idea of bench testing to see the difference in responsiveness, that's a solid idea.
I wonder if the inconsistency in voltage readings you saw in the first test might be due to responsiveness of the voltmeter. Perhaps an oscilloscope would be better for measuring small, transient voltages, as when measuring output from a crank position or cam sensor.
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