I’ve done this very thing using a microwave radar sensor instead. Positioned it behind the glass and used the standard PIR module which works without any additional configuration (just need to tell it the correct GPIO pin as standard). It was a RCWL-0516 sensor and there’s loads on ebay.

For anyone searching for this at a later date I managed to get it working using a sysvol npm. At the moment the module hides and shows based upon if the volume level has changed but I may trigger this through input from the rotary encoder itself.