Does setting a --proxy-server header work in chromeless?

Question

I'm trying to set the proxy server for a chromeless implementation on Lambda using the setExtraHTTPHeaders setter like:

await chromeless
       .setExtraHTTPHeaders({
                            '--proxy-server': 'xxx.xxx.xx.xx:80'
                            });

After merging I also tried by using:

chromeFlags: ['--proxy-server=xxx.xxx.xx.xx:80']

But the IP address is still the AWS IP. Does this setter not work or am I missing something?