How to add fields to display on Duplicate Check screen?

Hello, does anybody know how I can add more fields to this duplicate check screen?

It is actually on a custom module: Case Attachments.  We often have files of the same name in here and I would like to add the Case Number / (or Case 'Subject') to display in the list.

Is it a code change?  I didn't find anything via admin?

Many thanks,
Luke :-)

Enterprise. Cloud. Version 11.1.0.