Autoblog default thumbnail image add-on not functioning

I am having trouble getting the "default thumbnail image" add-on option to function properly. I am under the impression that by selecting an uploaded image from my media gallery in the "default thumbnail image" upload area, I have the option to replace the imported post's featured image with an image of my choice.

In practice, I am trying to replace the featured images from imported feeds with a standard "author" image for each feed. The idea is consistency.

Am I correct in assuming this plugin has that capability? If so, I would appreciate understanding how to harness that ability.