Thanks this was helpful in setting my RSS feed title in rss.xml:
<!--
If the page's .Title exists AND if it is not the same as the site's title,
set the title to
"Subsection title" on "My site title"
else, just
"My site title"
-->
<title>{{ with .Title }}{{ $title := printf "%s" $.Title }}{{ if not (eq $title $.Site.Title)}}{{$title}} on {{ end }}{{ end }}{{ .Site.Title }}</title>