What is the sensitivity slider set at? I would probably go for 30 percent if currently set at 50 percent. I would block out 1 additional square on the right side. If problems persisted I would probably put an outdoor camera above the door facing the Opposite direction basically.
I have a similarly shaped motion detection zone for a camera that faces major highway. Despite the fact that the highway is not part of the detection zone, every time a cop car goes by with its lights on it triggers the motion event. Shadows and unexpected light sources cause issues.