Why does the sky seem to be upside down?

I’m using CIE sky sunny with the sun, but the luminance shown in the image is weird.
At noon, the sun is at its highest point in the sky, but the luminance on the ground is higher. The sky seems to be upside down.
Here is the file. Have I done anything wrong?
fisheye.gh (54.1 KB)

I don’t know your 3D scene but the sky just seems to be brighter towards the horizon than it does higher in the sky, which seems fine, especially for a case where the sun is high in the sky and far away from the window.

I see. I thought the horizon would be less bright. Thanks, Chris!