Strange behaviour of shadow projector (from Standard Assets)

Hi, I’m using projector for showing fog of war (it’s quite big) and I observed that when I scroll my camera (it occurs for both in-game and editor camera) further from center of the scene, at certain point the brightness of the shadows casted by projector changes. The projector is in ortographic mode. Does anyone know how to fix this?

I’ve found out that placing a disabled (autoplay off) particle systems on the corners of the map prevents the brightnes change… Still, if someone know a proper solution to the problem, I would be grateful.