set AWS S3 config region in C++

I realized that when I have a .aws folder with config file inside it, AWS responds about 100 times faster (to any upload, download, or query) than when config file does not exist.

I do not want to have aws folder on my system, so I used the following code to set the config region. However, it is still not as fast as when config file existed.

Aws::Client::ClientConfiguration clientConfig;
clientConfig.region = "us-west-2";
Aws::Auth::AWSCredentials credentials("abcd", "abcd");
Aws::S3::S3Client s3_client(credentials, clientConfig);

What else needs to be set in the code to do what config file was doing?