Not familiar with how this system works.
I would assume that one of the devices is a projector and sends the light source to the other one which is the sensor?
If so, then wouldn't only the sensor needed to be shaded from outside light?
Perhaps switching sides so the sensor was on the shaded side, if there is one, would work?
Or moving it further away from the door opening?
Or a tube in front of it to provide the shade, like the tube extensions you might see on scopes?