sun reflection upon a rectangular steel surface

Hi, I'm an Italian student and I'm using Desktop Radiance in order to simulate an external wall enlighted by sun reflection upon a rectangular steel surface.
I can't understand why the reflection on the wall has a shape similar to a circumference instead of a rectangle.
I enclose what I did and I hope some of you could give me a suggestion.
Thanks.

                                                  Alessandro Bizzarri.

cameraDiProva.doc (69.5 KB)

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