Hi,
Yes, this has been done for 4.26 already. The radius slider can go down to 1km now, IIRC you can go lower, down to 100 meters but problems can start to show.
If you go with a lower radius, you will likely have to increase the sample count when tracing the atmosphere (to catch higher frequency details and planet shadows). There is now a quality slider on the SkyAtmosphere component that you can use.