site_url() does not work with alternate config

Hello guys i have 2 projects.
1 Front 
1 Admin

i have 2 separate folders for each project so in first project i have this config
FRONT Base_url = http://example.com
ADMIN Base_url = http://example.com/admin

In admin i want to use a config to create links for the FRONT

So i am trying to use this site_url with the Alternate configuration File

PHP Code:

$config = new \Config\AppFront();

echo site_url('test',NULL, $config); 


But it gives me the same URL for the admin
http://example.com/admin/test

Expected result
http://example.com/test

I have this Config File

PHP Code:

<?php namespace Config;

use CodeIgniter\Config\BaseConfig;

class FrontApp extends BaseConfig
{
    public $baseURL = 'https://example.com/';

    public $indexPage = '';

    public $uriProtocol = 'REQUEST_URI';
} 


Maybe this is a bug ? Or i am using this alternate config file wrong ?