Thank you for response.
I was aware of how the "Receive" function works and tested it several times, but accidently not with a second, visible fake sun just for atmosphere lightnings at the same place like the non visible surface lightning "main" sun.
+
My thoughts were also kinda: "Receive shadows from surfaces" checked works for any sunlights, regardless their individual settings..
I was wrong, thx for clarifying that Matt.
Hope our little dialogue will help other PPL too.
Greetings.. o/
Alex