Here's my dupe settings for individuals:
first name: length-5 weight-7
last name: length-5 weight-7
email: length-5 weight-10
Since contacts that are created via matching to UF only contain an email address and null name fields (or all unedited UF contacts if there's no profile setup), all of these contacts with emails of the same domain are considered as matching with the above settings. A match check shouldn't even be run in this scenario (should help performance too, as this could potentially exclude a lot of contacts).