My sensor triggers properly most of the time but seems to miss very wet snow.

Wet snow tends to fall at elevated temperatures. While it could be above freezing outside the colder upper atmosphere may allow snow to form. This occurs regularly in locations with a higher altitude. This is why the center position for the Trigger Temperature is 39 degrees rather than 32 degrees.

You can try adjusting the Trigger Temperature higher to activate the system when such conditions are prevalent.

Also, make sure that the sensor is not mounted in a location near exhaust hoods since this will increase the temperature whereby the control will not activate the mats.