There is an option in the settings:
Do not use Facebook avatars as profile images
And the explanation says: By default, the plugin will use Facebook profile images instead of your users avatars wherever possible. Enable this option to prevent this behavior.
I'm not sure why there isn't an option to prefer uploaded images rather than to have an either/or like you currently have. For our subscribers we want them to have their facebook profile showing.
Isn't there any way to say "If an author has a pic, then don't override it with their facebook pic."