Why is the internal shading effect better than the external shading？

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Why do I use the same type of curtains when setting up sunshade control in OpenStudio? The radiation from the external sunshade entering the room through the external window is higher than that from the internal sunshade, resulting in better performance of the internal sunshade than the external sunshade. It should be that the radiation from the internal sunshade entering is higher, right?