How to configure Nginx so the proxy_pass also aply to in-site requests?

Question

So let me introduce you to my context: I have a several containers deployed and I'd like to use nginx as reverse proxy so I can target my other containers (which are API's) through something like this: https://example.mysite.com/services/whatever_the_api.

I managed to get to a point where the proxy_pass works like a charm but now I have a problem: when my API admin page loads, it tries to find the assets like this : https://example.mysite.com/assets/... ditching the /services/api/ part.

Here is my /etc/nginx/config.d/sample.conf file :

server {
    listen myhost:80;
    server_name  myhost;
    location ^~ /services/apiName/ {
        proxy_pass http://myapp:1338/;
        proxy_set_header X-Forwarded-Host $host:$server_port;
        proxy_set_header X-Forwarded-Server $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }
}

If anyone knows what is the configuration material I'm missing, I'll be grateful to hear about it.