Can explain exactly what you mean by the actual string and the reference, what would the difference be 
This is what I mean. If you have a document with the pagetitle set to "My Blog" and you set the parameter like this:
The result would be the same as saying:
This will send Ditto looking for a TV named ’My Blog’ (’My Blog’ is the string value of the variable ’pagetitle’ for the current page) since there is no document field with that name.
What you want to do is tell Ditto to use the pagetitle field as the source for the sorting, and the returned value for pagetitle as the value to sort by. You could use any document or template variable as the sorting source (introtext, longtitle, id, alias,.) and Ditto will get the value for you.