I am experiencing the same problem. I have successful attempts in SOAP UI but unsuccessful attempts in c# environment. Are you suggesting that the fix is in the openSSL statement that you provided?
I had the same issue using c# (4.5.2). Just add the following lines before you send the request:
ServicePointManager.Expect100Continue = true;
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
request.ProtocolVersion = HttpVersion.Version10;