How to increase RPS in distributed locust load test

I cannot get past 1200 RPS no matter if I use 4 or 5 workers.

I tried to start locust in 3 variations -- one, four, and five worker processes (docker-compose up --scale worker_locust=num_of_workers). I use 3000 clients with a hatch rate of 100. The service that I am loading is a dummy that just always returns yo and HTTP 200, i.e., it's not doing anything, but returning a constant string. When I have one worker I get up to 600 RPS (and start to see some HTTP errors), when I have 4 workers I can get up to the ~1200 RPS (without a single HTTP error):

When I have 5 workers I get the same ~1200 RPS, but with a lower CPU usage:

I suppose that if the CPU went down in the 5-worker case (with respect to 4-worker case), than it's not the CPU that is bounding the RPS.

I am running this on a 6-core MacBook.

The locustfile.py I use posts essentially almost empty requests (just a few parameters):

from locust import HttpUser, task, between, constant


class QuickstartUser(HttpUser):
    wait_time = constant(1)  # seconds

    @task
    def add_empty_model(self):
        self.client.post(
            "/models",
            json={
                "grouping": {
                    "grouping": "a/b"
                },
                "container_image": "myrepo.com",
                "container_tag": "0.3.0",
                "prediction_type": "prediction_type",
                "model_state_base64": "bXkgc3RhdGU=",
                "model_config": {},
                "meta": {}
            }
        )

My docker-compose.yml:

services:
  myservice:
      build:
          context: ../
      ports:
          - "8000:8000"

  master_locust:
      image: locustio/locust
      ports:
          - "8089:8089"
      volumes:
          - ./:/mnt/locust
      command: -f /mnt/locust/locustfile.py --master

  worker_locust:
      image: locustio/locust
      volumes:
          - ./:/mnt/locust
      command: -f /mnt/locust/locustfile.py --worker --master-host master_locust

Can someone suggest the direction of getting towards the 2000 RPS?