The increase in CO2 as a percentage of the atmosphere correlates with the decrease in the the number of pirates (as any practising Pastafarian knows). But the decrease in the number of pirates has not caused the increase in CO2 as a percentage of the atmosphere (as any practising scientist knows).
What causes the CHT to go DOWN even though the EGT keeps going UP?
Balloon, okay so you have come up with a new version of the old "correlation is not causation" cliche. Fair point but we do not have a direct indication of the temperature of the exhaust valve and yet it is the hottest component in the engine and highly stressed so it is useful to know how it correlates with CHT and EGT.
Now, the APS hypothesis brought to us here by Walter Atkinson is
"valve temperature does NOT track EGT...[the NACA report with thermocouple in the valve] is definitive evidence the two are not in any way way related" is not supported by that report or any other piece of literature I have seen. The part of that report you and Walter both cite as definitive is the valve temp peaking slightly rich of EGT. But it does not follow that valve temperature does not track EGT. The correlation with EGT alone is a very good proxy for valve temperature as a function of mixture. When you add the influence of CHT (as indicated in figure 8 of that report by the spark plug bushing) it becomes apparent why the valve temp peaked slightly rich of EGT.
Now to illustrate the absurdity of Walter's logic let us also test the APS teachings against it:
"EGT is NOT the indication you're looking for. Pay attention to the CHT, and the valves take care of themselves.com." John Deakin; Fried Valves
Refer to figure 8 again. The CHT as represented by rear spark plug bushing. As a function of mixture it is going DOWN as the valve temp is still going UP. Now according to what you and Walter are saying this would be "definitive evidence" that CHT "does NOT track valve temperature and the two are in no way related". But of course, all it really means is that CHT - as a function of mixture - does not correlate with valve temperature as well on its own as it does when combined with EGT.
QED