Hi Dmitry,
I understand how and why this was setup the way it was. However, I do see an alternate approach that could cover the shadow switch without the need to separate surface and atmospheric light.
Transition Start Sun Angle
The main idea is that the sun should start dimming slowly, from the highest point in the sky on both surfaces and the atmosphere at the same time. This would tie together TSSA with Sun Elevation so the sun would reach 100,000 lux at 1pm and begin to dim slowly over time. This could also where the moon has slowly dimmed to 0 lux.
Transition Sun End Angle
This is where the Sun would reach 0 lux, well below the horizon based off the SUN DUSK OFFSET TIME (or whatever the natural angle of the sun would be about an hour to an hour and a half below the horizon. By this point the moon has reached it’s max 0.1 lux.
Transition Sun Middle Angle (Shadow Switch Only)
This is where the shadow switch would take place BELOW the horizon.
At this point, the sun would be far enough below the horizon that it would no longer be affecting surfaces above the horizon, so the shadows could safely be switched off on the sun. However, it would still be brighter than the moon on the environment, so auto-exposure would not yet be low enough to expose for the moon (which would still be fading on), hiding the shadow switch.
The much more intense value of the sun and the slower transition of intensity would allow for auto exposure to drop from 15EV to -5EV much more smoothly.
-Alex