Hi @Gef, try this:
$config['base_url'] = (isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == 'on' ? 'https://' : 'http://') . ($_SERVER['HTTP_HOST'] ? $_SERVER['HTTP_HOST'] : $_SERVER['SERVER_NAME']) . '/myfolder/';
notice the extra myfolder addition at the end. I’m not sure if this will work, I haven’t tested it, but you could try and report back. 
Good luck.