testrunner -h parameter

Hello,
I thought that the -h parameter is used to change the hostname of the url ?
for example, in my tests I have

http://<virtual ip>/v1/someservice.axmx

To test each server behind the virtual ip, I was hoping to do something like

testrunner.bat -h<server1> project.xml
testrunner.bat -h<server2> project.xml
tesrrunner.bat -h<servern> project.xml

However the logs indicate that -h<server n> has no effect. all the failed tests show that endpoint is set to virtualip.

What am I doing wrong ?

Thanks

Ali