Thermocouples produce a net voltage per unit length (The Seebeck voltage) that is proportional to the temperature gradient across that length. The use of a cold reference junction is the practical artifact or result of standardizing the reference conditions for thermocouples. Since the reference calibration tables do not specify a device’s length, one must realize that the net temperature gradient per unit length must sum up, or total to the temperatures referred to that at the hottest, wherever it is along the length.

Thermocouples do not measure at a point!. The hot point may be anywhere along its length, not necessarily at the warmer junction.