I have found that creating a metabox switch in the main content area allows me to set a default value "on" for that switch. However, if I move the location of the switch to the sidebar, my default value gets ignored, and the switch defaults to "off".
I do not see that issue on my demo site. The default value of the radio field should be a choice, not on/off. Can you please deactivate all plugins except Meta Box, MB extensions and switch to a standard theme of WordPress then check the issue again?