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A key feature of making the terrain shader look more natural as the sun light goes low is the Translucency options. These expand on the existing options explained here: PBR - Using Standard Shader#UsingStandardShader-Translucency.
In the Terrain shader there are now additional per Albedo scalars in the Translucency parameters section. These can be used to reduce the effect on areas with out grass for example.
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