You might be confused - as I was - about how to use the replacement variables that are offered to you on the Settings for your XPath XML parser page.
You need to put quotes around the variables in order to have them processed.
For instance my last field on this page offers:
The XPath query to run.
The variables $guid, $path_alias, $nid, $title, $field_file, $body, $created are availliable for replacement.
Since I needed the $path value and not the $path with the tags around it, I added the following to my text field:
Note, if you are having too much trouble making this work - you can also use REGEX to modify your field, if you've set up the Feeds Tamper module.