As long as the engine is being tuned for crisp and clean running and not lean running, the engines on your P-38 will run whatever temp they run at when they are happy. There is no hard set of rules to follow with two stroke glow engine temps. If they are getting too hot and fadeing or sagging in flight then richen them up, especially if airflow is a concern. You mention that you have 65 flights? did I read that correctly? If so, you are tuning them just fine (regardless of temp) as long as they have not been deadstick landings.
For a non competition single cylinder glow engine, the temp gun is merely a device to satisfy curiosity, nothing more.