Display Thumbnail image in Directory

I have yet to find a clear answer to this…

I have a Gravity Form, with an image upload – set as featured image – However, Directory only gives me the option of the full image or an icon.

I see in gravity-forms-addons.php that there is this line..
'postimage' => 'icon', // Whether to show icon, thumbnail, or large image
That would say to me that I should be able to set the image shown in a Directory to a thumbnail. I have tried to edit the file to be thumbnail, to no avail.

I have tried using “postimage” in the Directory shortcode, but that didn’t work, although it changed the Directory from the large image to an icon… that seems to indicate to me that “postimage” can be a valid shortcode, but that I don’t know the correct argument to access the thumbnail.

How the heck do I get Directory to show the thumbnail of a (featured) image uploaded in a Gravity Form?

Thanks!

https://www.ads-software.com/extend/plugins/gravity-forms-addons/