It wasn't obvious, but under the 'Home' tab in the Titles & Metas section, there's options for "Title template" and "Meta description template".
"Template" is the confusing word, but I think it's used to infer that you can include the %%sitename%%, %%sep%%, and other variables in these fields. But for those just adding text, it's a bit confusing. Please consider rewording that section in the plugin.