Just read this thread – https://kriesi.at/support/topic/wrap-box-shadow – because I wanted a shadow on my boxed layout as well. The thread said that it was impossible when using a background image. Well, I tried and indeed it doesn’t work with an uploaded background image. What I did then is this: upload a custom background image into the ‘images’ –> ‘background-images’ folder of the theme via ftp. Now I can chose my custom background in the theme options and still have a working shadow. Although you have to use ‘repeat’ and not ‘stretch’ for the latter will break it again. Learning as I go.
Probably already figured out by you guys but in case that you have not… ;-)