SkyAtmosphere and ExponentialHeightFog - Stationary or Movable?

Development Rendering
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1

Building a hybrid lit scene with Raytraced shadows and reflections and adding some atmospherics.
My sun is set to Stationary. 
​​​​​​​By default what should I set my SkyAtmosphere and ExponentialHeightFog Actors to?

2

As far as I know the SkyAtmosphere and ExponentialHeightFog Actors do not change based on their mobility such as Static, Stationary and Movable. I think it does not affect performance or visuals at all.

3

Thanks for the feedback