The exact flux orientation is complex, if you consider the geometry of Earth's umbra, penumbra ( and the antumbra). https://www.nasa.gov/image-article/diagram-of-umbra-penumbra/ - in addition to the seasonal axial tilt, etc. The Sun and the Earth are both spheres, so the radiation from the sun is not uniform within the solar disc, and the same hold for the Earth. So the terminator ( circle between 'night and day' ) isn't a perfect Great Circle, the tangent incidence occurs slightly offset into the night side.