Asp.net - Increasing Max Concurrent Connections For Web Service In IIS7 (load Testing)?

I'm trying to write a simple load tester for one of our web services, which is served through IIS7. I'm launching a load of threads (as Tasks) that call the web service as a Web Reference.Despite the threads all starting, only 2 concurrent connections from the app can be handled by the web service. I'm aware that by specification simultaneous connections are limited to 2 per user. For the sake of this load tester, which I guess is one user, I would like to open many simultaneous connections.I have tried to add the following to the web.config of the web service.

<system.net>
<connectionManagement>
<add address="*" maxconnection="40"/>
</connectionManagement>
</system.net>

My setup is as follows:

The web service is located at [URL], where MyWebServiceApp is configured as an application.The webmethod can be viewed as something trivial that simply waits for, say, 20 seconds before returning a response (making it easy to see that only 2 connections are open at any one time).The simplest form of the load tester code is ass follows:

Imports System.Threading.Tasks
Module SuperBasicLoadTester
Sub Main()

[code]....

I've tried pointing other load testing software (e.g. soapUI) at the web service and have observed the same issue.

Edits: I should add that the web service box is running Windows 2008 R2.Also I have run SoapUI and my loadtester simultaneously and each is only able to request 2 connections each (i.e. 4 in total).