Hi!
The problem in this case is, that combining the logic inbetween the fields (title, custom fieldst etc..) is not possible, as it is not treated as one single ‘bunch’ of data by mysql. There is the index table engine resolving this issue, but at the moment it only words with custom post types and attachments.
The AND logic in this case means, that all keywords should match, in at least one of the fields. Meaning that for example ‘donna napoli’ must both match either the title or the one of the custom fields (or any of the selected fields), which is not the case. This is due to the fact that it is not possible to check wether any of the keywords matches any of the fields in previous statements.
The only possible solution (if this is even possible), is to tweak the search query itself directly in the file. From what you described, you want all of the words, matching at least once, in any of the fields + matching the bio/title? It might be doable, I am honestly not sure.
If you can add temporary FTP and back-end access, I might be able to try to make a minor customization to the user search file, to see if this is possible in any ways.