Warm air rises. In a good forced air the fan stirs things up so it is the same temperature throughout but in a still air the temperature changes with the elevation. In a forced air the general recommendation is 99.5 F (37.5 C) throughout but in a still air the recommendation is 101.5 F (38.6...
I've done very well with my Genesis 1588 once I learned how to use it. It is more hand-on than some others.
I don't trust any built-in thermometer or hygrometer until they have been calibrated, even the ones for the high end makes and models. I don't trust the instruments from the store...
Most post office employees know very little about hatching eggs, like most of the general population. Also like most of the population they have some employees that don't like to follow rules but the majority at least try. Sometimes the problem can be with the person shipping the hatching...