4k data limit on wwwform post?

You can upload more than 4k via WWWForm(), even on iOS, just tried it. I'm streaming a 25k file like this (inside a coroutine):

 WWWForm postForm = new WWWForm();
 postForm.AddBinaryData("theFile", buffer, localFileName, "text/plain");
 
 WWW upload = new WWW(uploadURL,postForm);        
 yield return upload;
 
 if (upload.error == null)
    Debug.Log("Upload done: " + upload.text);
 else
    Debug.Log("Error during upload: " + upload.error);