Oh, well...
I've seen almost all CG Sky models being limited by a simple human flaw - a predisposition that planets are flat, thus horizons are straight flat also - but, since i prefer real truth, i mimic nature >>>
Earth Curve Calculator ;)
BTW, i think more advanced Environment model is needed in Corona (especially for architectural viz!!!), with added settings & options for atmosphere, haze, color shift, ground, reflection, shadow intensity, horizon height, blur and curvature... better naming conventions (azimuth, zenith..), supporting multiple skies and suns... would be of great benefit to everyone. Similar to that which iray uses (tho it has no limb darkening) ;)
... and it's recorded in real time...