Spirent TestCenter 5.13 - RFC2544 Latency test relative to Throughput

In the RFC2544 wizard, I have selected both Throughput and Latency test. Under the options to configure Latency test, there is no parameter to set the Latency test to run relative to the throughput for all the frames and not what is set in the Step Start option.

How can I set the latency test to run relative to the throughput.