It depends. Let's start:
If you mean sky shadows... then increase LSM, as the sky is being treated as a direct light for more efficient sampling.
If out mean sky GI bounces, you may increase AAvsGI.
There is one bad Noise source though: the floor reflection from sun to a ceiling. This is the first bounce and the first bounce is 100% pathtraced and does not rely on UHD. Meaning with a strong sun, the first bounce off the ground will result in slower sampling vs the rest of the scene. No way around it, but increasing AAvsGI. Don't over do it however, adaptivity will recognize it and gi sample these things harder. Going over 32 AAvsGI will result in slower adaptivity response due to missing image samples.
If you have unreasonable amount of noise, post a render and someone will take a look at it, or simply refer to the corona help desk for general noise info
https://coronarenderer.freshdesk.com/support/solutions/articles/5000501983-how-to-get-rid-of-excessive-noise-Lastly: there is the portal friction value in the dev/debug section. Don't change it, as the value has been found to be optimal by the devs. Simply setting portals correctly up according to:
https://coronarenderer.freshdesk.com/support/solutions/articles/5000501660-how-to-use-light-portals-in-corona-Is already enough
