This behavior display a region in the page if the image/file you select from the recordset exist on the server.
The suffix is used when you want insert the thumbnail of an image, when you insert a generic file the suffix is not necessary.
If you insert the suffix the behavior search for the thumbnail, othervise search for the big image.

This behavior has 2 method to work: show a region if a file exist or if not exist

The suffix of the image thumbnail. The suffix position is not requested because the behavior search before with the suffix between the image name and the image extension and if the thumb is not find search with the suffix before the name.