I don't know why, but it always feels like when someone near me as the shade open the sun lines up directly in my eyes. Even worse was a flight I had returning from ORD where I was getting sun reflection from a tablet from the other side of the plane.
Its almost feels like the person at the shade has a good balance, as their eyes are typically shaded from the direct light but it provides good ambient light.... but for those directly in the suns "firing line" it can be quite uncomfortable.