Response Time Vs Time Taken by Test Case

Hello!

I want to assert the response time of a soap request. Running my test as a functional test everything is OK using "Response SLA" Assertion.

Now I need to perform Load test with the same goal, and I thought that "Step Maximum" assertion would fix to me, but it seems that the returned values (min, max, avg, etc..) are related to the Time Taken property of the test case, not to the response time of the soap request. I have deactivated assertions and the two properties of "include request in time taken" and "include response in time taken" both in the global settings and in the test case settings, but the time taken is always more than one second greater than response time of the soap request, which is unnaceptable for my purpuses:

-Is there any way to reduce the time taken property just to be equal to the response time of the Soap request?

-would be LoadUI valuable for me to perform this task? I don't want to move from SoapUI in principle...

Thanks in advance!!!