I just purchased a model 600 with the automatic humidity control. I do not have a return duct. I was planning on running a 6\" duct from the unit to the inside of the filter box to make the unit work. I noticed the model 60 controller says it needs to be mounted on the return duct. Why can this not be mounted on the wall near my thermostat. I would think if I used stand-offs to allow air to get to the sensor this would work the same. Does the sensor need active air flow to work or would it still register the humidity if mounted on the wall? I would rather use the automatic function rather than the manual mode for obvious reasons.