Terrain is treated like a model in A7, isn't? So it still affected by static light and shadow but it affect the entire part of the terrain. Use dynamic shadow and light instead, or use prebaked shadow(though I cant find the way in 3DGS for that:p)
- sometimes the terrain is lighted without sun and dynamic light ??? - sometimes models are lighted by static lights, sometimes not ??? - dynamic light only lights parts of a model ???