Setup_remote_docker version does not support dynamic values?

I couldn’t find this documented anywhere, but is the version attribute limited to static values only? I’m basically getting this output that looks like variables aren’t being interpolated like other steps would normally?

Allocating a remote Docker Engine
Requesting version: ${docker_version}

failed to create host: rpc error: code = InvalidArgument desc = Image docker-${docker_version} is not supported

I tried other variable names in case DOCKER_VERSION collided with another, but no luck. My job configuration essentially looks like this:

    type: env_var_name
    description: Remote docker version to setup for docker builds.
    default: DOCKER_VERSION
  - docker/install-docker:
      version: v${<< parameters.docker-version >>}
  - setup_remote_docker:
      version: ${<< parameters.docker-version >>}

Using the latest circleci/docker orb, the docker/install-docker works fine. If I hard-code the version given to setup_remote_docker it works fine. The version I’m targeting is 19.03.14

Am I doing something silly?