Force Omeka to display particular derivative in Media record

We are importing images via a url from our Archives system - the images have persistent url that includes a .php extension. We can get them to import by disabling the file validation Omeka-S and they display fine. If you click on the image to enlarge it, you see text and not the enlarged image because Omeka-S has created a version of the original with the .php extension.

Is there a way to force Omeka-S to display the ‘large’ derivative version of the image and not the original. Or is there a way of preventing Omeka-s appending the php to the orginal that it creates.

We’re new to Omeka-S and looking to use it to create exhibitions derived from a range of originating systems.
Any insight would be appreciated.