That's a good point. If you get notification that the camera is triggered, and you check the video and see the camera is covered, then it would be safe to assume, it's not a Amazon delivery.
If his porch ceiling is higher than 7 feet, just mount the camera up at the ceiling line. Someone would have to grab a chair or ladder to cover the camera, and just like my first paragraph, you'll instantly know if it's Friend or Foe.
Plus, being tucked up at the ceiling line will help with glare and IR issues.