addColumn yii migration position

This should work!

$this->addColumn('table_name', 'column_name', 'type AFTER column6'); 

examples:

$this->addColumn('tbl_posts', 'email', 'VARCHAR(150) AFTER `name` ');
$this->addColumn('tbl_posts', 'phone', 'string AFTER `email` ');

$this->addColumn('{{%user}}', 'username', 
            $this->string()->notNull()->unique()->after('id')
            );