Force "full" shadow?

Hi guys, I have a “problem” regarding shadows.

I have a window. I’d like to have this window to cast a “full” shadow instead of a “masked” shadow.
It’s hard to explain. I want to use a Spotlight with a lightfunction to simulate the shadow of the window for visual reasons.
It looks weird If I use a lightfunction and the “real” shadow is still visible.

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Is there a possibility to make the window cast a “complete” shadow?

You can put a flat static mesh in front of it with “Cast invisible shadows” and possibly “Actor is hidden in-game” set to true, so that it blocks the sunlight but still lets you see the sky. Is that what you’re trying to achieve?