When writing XPath, specify what you want, not where it is.   If you are interested in the content of <c> nodes, i.e. regardless of where they might be found, then ask for that.   Don’t code the search “from the outside in,” based on your personal knowledge of the structure.

You might find it simplest to let at least your first stab at the XPath expression locate all of the nodes, with your Perl code then looking for multiple spaces within the body.   Then, if necessary and warranted, you can refine the expression to look for the spaces.