oggers,
You seem to be missing the point and confusing some things.
1. The centre of valve crown thermocouple is tracking the EGT more closely because it is basically an EGT probe. Look at where they positioned it
You are not looking at the relevant trace for a start.
2. The valve temperature that matters is the valve face/seat and the one represented by the back of the valve body. Stick to the important ones and don't confuse the two.
Please refer to my previous post about what happens when you advance the spark. ICP goes up, CHT goes up, valve temperature goes up and EGT goes down.
Next and for those who say APS never give anything (data) for free here is a slide from the APS class. Look closely at the Cylinder 6 trace in blue. Note that the CHT is going through the roof. The ICP was definitely going through the roof (not shown but we know) and correspondingly the EGT fell considerably. What do you think the valve temperature was doing at the seat/face and the bulk of the valve body? Please answer this.
Courtesy of Advanced Pilot Seminars
Your position has been that EGT is driving valve temperature, and that seems to be based on CORRELATION not CAUSATION. There is correlation for sure on the curve you keep showing above. However this is the wrong curve being observed in terms of an exhaust valves overall temperature and health. The appropriate one is the valve face/seat and the body represented by the back of the valve.
So Correlation some of the time does not support the facts. Causation is not from EGT, as has been shown in the NACA report on page 44 where EGT did not drive the valve temperature.
It is worth repeating, ICP is what drives valve temperature, and when you have high ICP you get high CHT, always. This is the best proxy you have for valve temperature in your plane. As is shown in the picture above.
Walter……anything to add? John Deakin perhaps?