docker-compose: Connect container to "network=host" and to other services

Question

I struggle to achieve the following:

I want two have two docker compose services (let's call them service_A and service_B), where

• service_A needs to be in the host's network (i.e. runs with network_mode=host) and
• service_B can connect to service_A via its hostname, but it's also in the hosts network.

Here I made an example, which demonstrates what I want to achieve with postgres services as examples:

version: '3'

services:
  service_A:
    image: postgres
    environment:
      - POSTGRES_PASSWORD=password
    network_mode: host  

  service_B:
    image: postgres
    depends_on:
      - service_A
    network_mode: host 
    command: psql postgresql://postgres:password@service_A:5432 --command "select * from pg_tables limit 1;"

But, when setting network_mode=host on service_A and service_B, service_B cannot reach service_A via its hostname. Is there an easy way to achieve that?

For those, who are interested why I need such a setup:

• service_A functions as a proxy and logs into a VPN (via the docker host's connection)
• and service_B shouldn't see the whole docker host, but needs to read from service_A, but be also responsive on the docker host.