There are several reasons, but the main one is that the Thermal Gradient Ring (TGR) is not a 2 point test as 12 different temperatures are in the corridor in duplicate.
Moreover, the amount of outcomes is way larger, including entry time, time spent, travel distance, preferred temperature.
Learn more on Thermal Gradient Ring: https://ugobasile.com/products/categories/pain-and-inflammation/new-thermal-gradient-ring-tgr-zimmermann-s-method-2-0
Learn more on Thermal Place Reference: https://ugobasile.com/products/categories/pain-and-inflammation/thermal-place-preference-for-mice-and-rats