Right now, I can see the last 5 test runs in the Traffic Viewer. I want to see more, but I can't find the place to configure the number of payloads available, or even if it's configurable.
The limit for how many runs are shown in the Traffic Viewer tool is not user configurable. The Traffic Viewer tool is only intended for manual inspection when manually running tests from the SOAtest workbench UI. For automated testing, like from soatestcli, you collect traffic differently by configuring SOAtest to generate reports which include traffic. Parasoft reports can be archived as needed for seeing past test results including traffic from past test runs.
The following that I am about to mention is totally unsupported internal API and is therefore not guaranteed to work any time the future, but you can modify this integer from a script, like something you run from an Extension Tool:
As you might guess, this TEST_RUN_LIMIT field is initialized to 5. Just assign to something else from a script in an Extension Tool.
Please keep in mind that if you try to use this unsupported undocumented internal API, you may run into memory problems if you set the value so high that you start saving more traffic data than you have memory for. Parasoft does not recommend setting this value.
Recent versions of SOAtest manage memory for traffic runs in a very intelligent and optimal way so as not to significantly blow up memory usage. There should be no issue but I do not want to understate the fact that this is still totally unsupported. Using undocumented, internal APIs is never officially supported and therefore never officially recommend by Parasoft.