I was looking at what was causing the slow down, and it was the favicon.
I hadn’t defined its location, name or anything about it and the results were going out and looking for it on its own. And including it in the test.
I moved it off to a CloudFront CDN and made both the .ico and .png versions available using the CDN, and then also put in a “dns-prefetch” link so that it can resolve that CDN as quickly as possible and our TTFB went down by a single MS. No big deal.
But at least the favicon (which is typically called upon by the browser AFTER the page is loaded) won’t get in the way of our tests.