How to view IP of upstream server when load balancing?

I've added a second plex server to another machine on my local lan so if the first one goes down for any reason it'll load the second one as a backup. Now, when viewing the logs I want to be able to see which IP it was sent to. Here's what I have so far:

The upstream and log code in plex.subdomain.conf:

upstream plex-resolver {
    server 192.168.0.195:32400;
    server 192.168.0.194:32400 backup;
}

# TODO: $proxy_host isnt really what I want;  I want to see exactly which pms server it went to.
log_format plex_access '[$time_local] $remote_addr - $host -> $upstream_addr (SentTo: $proxy_host): $request $status upstream_response_time $upstream_response_time msec $msec request_time $request_time tst: $upstream_http_server';

# Send Plex-only traffic to it's own log for easier viewing.
map $host $pms {
    default 0;
    ~*^plex 1;
}

access_log /config/log/nginx/plex_access.log plex_access if=$pms;

Code (markup):

and the code sending to the resolver:

set $upstream_app plex-resolver;
set $upstream_proto https;
proxy_pass $upstream_proto://$upstream_app;

Code (markup):

I want the "SentTo:" to always show me the exact IP of the endpoint it was sent to, but it just shows the name of the upstream block instead:

[10/Mar/2022:23:32:20 -0600] 10.0.0.2 - plex.<redacted>.rocks -> 192.168.0.194:32400 (SentTo: plex-resolver): GET /?X-Plex-Token=<redacted> HTTP/2.0 200 upstream_response_time 0.000 msec 1646976740.193 request_time 0.008
[10/Mar/2022:23:32:23 -0600] 10.0.0.2 - plex.<redacted>.rocks -> - (SentTo: -): GET /?X-Plex-Token=<redacted> HTTP/1.1 301 upstream_response_time - msec 1646976743.577 request_time 0.000 -
[10/Mar/2022:23:32:23 -0600] 10.0.0.2 - plex.<redacted>.rocks -> 192.168.0.194:32400 (SentTo: plex-resolver): GET /?X-Plex-Token=<redacted> HTTP/2.0 200 upstream_response_time 0.010 msec 1646976743.747 request_time 0.009
[10/Mar/2022:23:32:24 -0600] 10.0.0.2 - plex.<redacted>.rocks -> - (SentTo: -): GET /library/sections?X-Plex-Token=<redacted> HTTP/1.1 301 upstream_response_time - msec 1646976744.596 request_time 0.000 -
[10/Mar/2022:23:32:24 -0600] 10.0.0.2 - plex.<redacted>.rocks -> 192.168.0.194:32400 (SentTo: plex-resolver): GET /library/sections?X-Plex-Token=<redacted> HTTP/2.0 200 upstream_response_time 0.000 msec 1646976744.752 request_time 0.006
[10/Mar/2022:23:32:34 -0600] 10.0.0.2 - plex.<redacted>.rocks -> 192.168.0.195:32400, 192.168.0.194:32400 (SentTo: plex-resolver): GET /?X-Plex-Token=<redacted> HTTP/2.0 200 upstream_response_time 21.040, 0.010 msec 1646976754.110 request_time 21.052
[11/Mar/2022:00:00:55 -0600] 10.0.0.2 - plex.<redacted>.rocks -> 192.168.0.195:32400, 192.168.0.194:32400 (SentTo: plex-resolver): GET /library/sections HTTP/2.0 200 upstream_response_time 21.040, 0.010 msec 1646978455.131 request_time 21.047

Code (markup):

Does anyone know how to do what I'm looking for?