Nginx normalize Accept-Encoding for better cache hit ratio - nginx

Question

I have problem with normalizing Accept-Encoding, during tests express server getting correctly normalized Accept-Encoding from nginx, but nginx didn't respect "Vary: Accept-Encoding" and when I send request with e.g. "Accept-Encoding: gzip, br" and "Accept-Encoding: gzip" I got 2 requests to express server, it should be only 1 request
nginx
proxy_cache_path /tmp/express_cache keys_zone=express_cache:10m levels=1:2 inactive=600s max_size=100m;
map $http_accept_encoding $pwa_normalized_encoding {
default "";
"~*gzip" "gzip";
}
server {
listen 80 default_server;
listen [::]:80 default_server;
server_name _;
set $pass_access_scheme $scheme;
set $pass_server_port $server_port;
set $best_http_host $http_host;
set $pass_port $pass_server_port;
location /express {
proxy_set_header Host $best_http_host;
proxy_set_header X-Forwarded-Host $best_http_host;
proxy_set_header X-Forwarded-Port $pass_port;
proxy_set_header X-Forwarded-Proto $pass_access_scheme;
proxy_set_header X-Original-URI $request_uri;
proxy_set_header X-Scheme $pass_access_scheme;
proxy_set_header X-Original-Forwarded-For $http_x_forwarded_for;
proxy_cache express_cache;
proxy_cache_lock on;
proxy_cache_background_update on;
proxy_cache_use_stale error timeout updating http_500 http_502 http_503 http_504;
proxy_cache_min_uses 1;
proxy_set_header Accept-Encoding $pwa_normalized_encoding;
add_header X-Cache-Status $upstream_cache_status;
proxy_pass http://localhost:5000/;
}
}
express server
app.get('/', (req, res) => {
console.log("encoding:", new Date().toISOString(), (req.get("Accept-Encoding")));
res.setHeader("Cache-Control", "public, max-age=30");
res.setHeader('Content-Type', 'application/json')
res.setHeader("Vary", "Accept-Encoding");
setTimeout(() => {
res.json({date: new Date().toISOString()})
}, 300)
})