Settings for Automatically Created Accounts

Your screenshot show the site-wide settings for all apps.

The form you're looking for is the application-specific settings for just that one app. You'll find it under admin >> site building >> facebook apps, then click the 'edit' link for your app. Then expand the user settings fieldset.

I can see how this is confusing. If anyone is up to the task, I'd commit a patch that adds links from one form to the other. That should make both forms easier to find.