Please note that the magnet inside the magnet housing is not centered (see picture below). Thus, the side with the notch in the housing (that's where the magnet sits) should ideally face towards the sensor when mounting the magnet.
The picture below shows the correct orientation of the magnet. The side of the magnet with the small notch faces towards the side of the sensor with the small blue LED (which blinks when it sends a message).
The picture below shows the side of the magnet housing with the small notch indicating where the magnet sits.