Isn't the whole point of a reverse proxy to use FQDN instead of IP:port? Why would you monitor IP:port in that case? You want to know if you're unable to access your service, if you're monitoring IP:port and your reverse proxy shits the bed, then Uptime Kuma will happily report everything up and running. If you're monitoring FQDN and either your service dies or your reverse proxy dies, UK will notify you your service is unreachable, granted if your RP dies UK will alert you everything is down, which is also more helpful as you can narrow down the issue.
Isn't the whole point of a reverse proxy to use FQDN instead of IP:port? Why would you monitor IP:port in that case? You want to know if you're unable to access your service, if you're monitoring IP:port and your reverse proxy shits the bed, then Uptime Kuma will happily report everything up and running. If you're monitoring FQDN and either your service dies or your reverse proxy dies, UK will notify you your service is unreachable, granted if your RP dies UK will alert you everything is down, which is also more helpful as you can narrow down the issue.