Highest EGT's are supposed to occur about 6 inches (20 cm) past the exhaust valve. As mentioned above this is partially due to the rich fuel mixuture continuing to burn as it exits the exhaust valve and the transition from the watercooled cylinder head into headers that have have very limited cooling. The rise in exhaust temp with richer mixtures also depends on where you are on the AFR curve. If you are running lean richening the mixture will cool down EGT's if you are rich of max power adding fuel can increase EGT's.
Part of the answer is why are you using the EGT gauge. In aircraft they put it infront of the turbo and watch the Turbo Inlet Temp (TIT), They also have Cylinder head temp sensors on the air cooled aircraft engines.
On autos most folks put it a few inches down the exhaust runner and are watching max Exhaust gas temps.
On the WRX max rated turbo inlet temp is 1625 degrees F according to the turbo manufacture (mitsubishi), most folks get nervous when EGT's taken in the exhaust header just outside the port read over 1600 deg F.
Larry
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