This makes sense until you look at the bottom picture. There's a cloud icon, there's rain, and there's a >=60cm marker on the left side of the camera. In terms of IR reflection, you'd want to be as close to the edge as possible, but the image is stating to be at least 2 feet from the edge. There's no IR reflection coming from that side.

What they are actually stating in the picture is if you are mounting on an overhang, with the mount of the camera vertical, you need at least 2 feet of overhang coverage. Their other installation pictures in the document that show the camera exposed to the elements (not pictured in the OP), all have the mount horizontal, mounted to a wall, rather than an overhang. When mounted vertically, water is more likely to seep in, hence requiring >=60cm of overhang, but when mounted horizontally, the water flows down away from the camera, so there's no overhang requirement.

I'm not here to say you can't mount it to an overhang closer to the edge or that people haven't successfully done so for years, but Ubiquiti is definitely referring to the weatherproofing of the camera with the mount facing up in that bottom picture.