contacts duplicate check

Hi. I'm trying to modify the duplicate check filter for Contacts module.

I'm using the instructions at https://support.sugarcrm.com/Documentation/Sugar_Developer/Sugar_Developer_Guide_12.0/Architecture/Duplicate_Check/

and have added the code below to the location ./custom/Extension/modules/Contacts/Ext/Vardefs/duplicate_check_email_v7_twitter.php

The example removed the 'shipping_address_city' field, I have tried to use the same theory to add the 'twitter' field to test with but as far as I can tell it has made no difference.  

Can any of you see what the issue is please?

<?php

$dictionary['Contact']['duplicate_check']['FilterDuplicateCheck'] = array(
    'filter_template' => array(
        array(
            '$and' => array(
                array('twitter' => array('$starts' => '$twitter')),
                array('first_name' => array('$starts' => '$first_name')),
                array('last_name' => array('$starts' => '$last_name')),
                array('accounts.id' => array('$equals' => '$account_id')),
                array('dnb_principal_id' => array('$equals' => '$dnb_principal_id')),
            ),
        ),
    ),
    'ranking_fields' => array(
        array(
            'in_field_name' => 'twitter',
            'dupe_field_name' => 'twitter',
        ),
        array(
            'in_field_name' => 'account_id',
            'dupe_field_name' => 'account_id',
        ),
        array(
            'in_field_name' => 'last_name',
            'dupe_field_name' => 'last_name',
        ),
        array(
            'in_field_name' => 'first_name',
            'dupe_field_name' => 'first_name',
        ),

    ),
);

Also, would the updated duplicate check happen at the point of entry like it currently does if it matches a name, or is this for the 'Find Duplicates' you can run when in a record?

Thanks
James