http4s - how create blaze client with limited count of threads?

I trying to create blaze client with limited number of threads like this:

object ReactiveCats extends IOApp {
  private val PORT = 8083
  private val DELAY_SERVICE_URL = "http://localhost:8080"
  
  // trying create client with limited number of threads
  val clientPool: ExecutorService = Executors.newFixedThreadPool(64)
  val clientExecutor: ExecutionContextExecutor = ExecutionContext.fromExecutor(clientPool)

  private val httpClient = BlazeClientBuilder[IO](clientExecutor).resource

  private val httpApp = HttpRoutes.of[IO] {
    case GET -> Root / delayMillis =>
      httpClient.use { client =>
        client
          .expect[String](s"$DELAY_SERVICE_URL/$delayMillis")
          .flatMap(response => Ok(s"ReactiveCats: $response"))
      }
  }.orNotFound

  // trying to create server on fixed thread pool
  val serverPool: ExecutorService = Executors.newFixedThreadPool(64)
  val serverExecutor: ExecutionContextExecutor = ExecutionContext.fromExecutor(serverPool)

  // start server
  override def run(args: List[String]): IO[ExitCode] =
    BlazeServerBuilder[IO](serverExecutor)
      .bindHttp(port = PORT, host = "localhost")
      .withHttpApp(httpApp)
      .serve
      .compile
      .drain
      .as(ExitCode.Success)
}

full code and load-tests  

But load-test results looks like one thread by one request:

How I make restrict numbers of threads for my blaze client?

Copy from my commment.

Answer for performance issue is properly setup for Blaze client - for me this is .withMaxWaitQueueLimit(1024) parameter.