It is measuring the heat at the front part of the chamber, to describe it it is like a hair dryer from hell. the glass of the chamber holds alot of heat so I think the beans get the actual heat but more of a wash of heat rather than the constant of a oven or the like. Like brewing beer it(time and temp) depends on the process.I rely on the thermometer on my roaster, gene cafe.
I think crack depends on the process rather than the temperature, but we are roasting in a differernt way. An apples to oranges roasting method.
I see, your roaster is probably measuring the temp of the roaster rather than emerged in the beans. I can certainly see that being much hotter than the bean temp.