First, I want to share the datasheet for the Bosch sensor to emphasize the importance of the tightening torque, the imperative to not use any washers between the sensor and the engine, and the need for a clean, flat mounting surface.
https://www.bosch-motorsport.com/content/downloads/Raceparts/en-GB/51782795118019851.html#/Tabs=51794187/
The sensor is a quartz crystal that produces a charge output when mechanical pressure is applied to it. The charge gets converted to a voltage with a precision capacitor. Ideally, the mechanical pressure is applied by a mass of metal that is moved by the vibration of the engine structure associated with engine knock. If you mount it on a non-flat mounting surface, such as a washer or a dirty mounting pad and/or you tighten it too much it will produce an offset voltage that is always there, whether the engine is knocking or not. So there is that.