When using Calibre-Web from Docker, the most popular container doesn't offer an obvious way to set up a reverse proxy under a different base URL. It's simple to do by writing a request header in your reverse proxy config, as demonstrated below.
<Location "/calibre/">
ProxyPass http://127.0.0.1:8083/
RequestHeader add X-Script-Name "/calibre"
</Location>
location /calibre/ {
proxy_set_header X-Script-Name /calibre/;
proxy_pass http://127.0.0.1:8083;
}