Using BTCPay Server along with a web server in a single machine

For better context: https://stackoverflow.com/questions/63123652/is-there-a-way-to-set-port-in-a-dns-forward

Hello community! I have setup an aws ec2 instance and installed BTCPay server on it. I used the Docker version.

I also bought a domain name and pointed btcpay.example.com to my BTCPay server with an A record.

I want to run a Web server along side BTCPay server at example.com. BTCPay Server has already taken up port 80 and 443 so I guess I’ll have to run my web server on another port but how can I specify port number in a DNS record?

With some help I learnt about reverse proxy and I see BTCPay server has an environment variable called "REVERSEPROXY_DEFAULT_HOST: Optional, if using a reverse proxy nginx, specify which website should be presented if the server is accessed by its IP." though I don’t understand how to configure this or if its the correct way.

Help please?