TTFB and Content Download time calculation for HTTP2 Server Push

We’ve been running WPT for an HTTP2 site that has Server Push.

The “Time to First Byte” and “Content Download” times for images that are pushed do not match up with the times we are seeing for the same images in tcpdump traces for the same test.

I tried to find the documentation explaining how these two times are calculated for HTTP2 Server Push scenario, but could not find any.

Also, I don’t see these two KPI’s in Chrome browser’s time waterfall for pushed images when I load the same site in Chrome browser.

Can someone help explain how these metrics are calculated by WPT for HTTP2 Server Push case ??