The "ns" parameter specifies which is the root namespaces where the plugin will create the pages. If you want it below the ":8-social:8.7-playground:" namespace you have to use the following syntac:
{{yearbox>year=2011;size=10;ns=8-social:8.7-playground:yearbox;name=day}}
(Based on the information which are on the plugin page. Don't know if it works.)