CHT Thermocouples

I know of two kinds of CHT thermocouples - the ring type which attach at the
spark plug and the probe type which thread into a fitting on the cylinder.

Conventional wisdom is that the ring type will show significantly higher
temperatures than the probe type. I've seen differences reported as up to
50F between the two types.

Anyway, Lycoming (and Superior, and TCM, and everyone else) has
recommendations on minimum, maximum, and ideal CHT's. Which type of
thermocouple are engine manufacturers and experts referring to when they set
CHT guidelines?

KB