First Interactive aka First CPU Idle Calculation

Hello together,

i put this in “Bugs/Issues - Seeing something not behaving like you would expect?” hope this is correct if not please tell me and I move it somewhere else.

On quite some tests I noticed that for the “Time to Interactive” Calculation I would expect a other value and m assumption would be that the Interactive window seems not correctly determined. Let me explain on a example:

For the KPI “First CPU Idle” was First Interactive I would expect:
"Time to First CPU Idle (was First Interactive) Calculation

  1. Start looking for First Interactive at first contentful paint
  2. Look for the first interactive window (with no regard to in-flight requests)
  3. First Interactive is the start of the interactive window from step 2, first contentful paint or DOM Content Loaded, whichever is later"
    “Interactive Window
    The browser’s main thread is considered “interactive” when it is not blocked for more than 50ms by any single task so it will be able to respond to user input within 50ms. An interactive window is a period of at least 5 seconds where there are no main-thread tasks that take more than 50ms.”

For the concrete Test (see attachment):
I would expect a “First CPU Idle” time around 12.4sec and not like 9.141s (correlating with the DomContentLoaded event - but at this time the main Thread seems still busy)

How do you see that ? would be thankful to point out any mistakes in my interpretation.
NG Michael