How can I make concurrent requests faster with Retrofit / OkHttp?

Question

I need to make 50 http GET requests as fast as possible with Retrofit in Android. I am using Retrofit with OkHttp. Currently Retrofit is doing a poor job vs plain Java ThreadPoolExecutor and HttpUrlConnection: about 50sec for Retrofit and 30sec for plain HttpUrlConnection for all 50 requests, if I set the pool size 20 for ThreadPoolExecutor and for Retrofit / OkHttp I set okHttpClient.dispatcher().setMaxRequests(20);.

If I look at logcat I can see that Retrofit is doing maximum of 5 concurrent requests no matter what I set in setMaxRequests() while with ThreadPoolExecutor there are as many concurrent requests as there are available worker threads.

Is there anything I can do to make Retrofit faster? I don't want to switch to HttpUrlConnection because Retrofit is so elegant and easy to use.

Edit 1

I tried providing custom ThreadPoolExecutor to OkHttp but no time improvement from this:

OkHttpClient.Builder builder = new OkHttpClient.Builder();
ExecutorService exec = new ThreadPoolExecutor(20, 20, 1, TimeUnit.HOURS, new LinkedBlockingQueue<>());
Dispatcher d = new Dispatcher(exec);
builder.dispatcher(d);
OkHttpClient okHttpClient = builder.build();
okHttpClient.dispatcher().setMaxRequests(20);

Edit 2

I make all requests to the same endpoint, if this matters

Answer 1

Since they are all going to the same host, have you tried:

okHttpClient.dispatcher().setMaxRequestsPerHost(20);

Dispatcher.setMaxRequestsPerHost