Hi Graham

Thank you for reaching out to us.

You can achieve this by increasing the screen size of mobile and tablet devices set in the main wpDataTables settings.

This will show the + button for all screen sizes lower than what you set in the settings, so setting a very high number would be the best.

Since this is in global settings it is applied on all tables. We have in plan to implement it on each table on Customize tab in table settings in the future.

Until that you can use this hook in functions.php of your theme or child theme

// $tableDescriptionObj std class/object thatcontain all table description
// tableId string that contain table id
// wpdtObj WPDataTable object function updateTableDescription( $tableDescriptionObj, $tableId ,$wpdtObj)   {        // condition for table that have id 1     if( $tableId == 1 ){        // set tabletWidth on 1000 you will insert value for your needs            $tableDescriptionObj->tabletWidth = '1000';        // for mobileWidth you will use like this        // we set 300 you will set for your needs            $tableDescriptionObj->mobileWidth = '300';        }    return $tableDescriptionObj;
}
add_filter('wpdatatables_filter_table_description','updateTableDescription', 10, 3);

I hope this helps, do let us know if you need any further assistance. 

Hi Graham

This looks fine to me but do let me know if you encounter any issues so we can troubleshoot further.