(SU2019 Enscape-2.6.0-preview.8+10829)
My default atmosphere settings are with sunlight at 80% and 100% cloud density. I normally use the forest drop-down as a horizon source (rather than a skybox).
As the time shifts the horizon image only lightens enough to be seen properly when the sun flashes through a breaks in the clouds(*).
(*This still annoys me: how can the sun break through when there is 100% sun coverage?)