Why RF exposure evaluation depends on how much field strength actually reaches a person, and several things determine that. Frequency matters because the FCC MPE limits change with band (the human body absorbs most efficiently around 30-300 MHz, so the limits are strictest there), and power level sets how much energy is radiated in the first place. Distance matters because field strength falls off rapidly as you move away from the antenna, and the antenna's radiation pattern and gain determine which directions get the concentrated energy. All of these go into the station evaluation required by Part 97.13(c).
Watch out Each individual choice is a real factor, but picking just one ignores the others; an exposure calculation needs frequency, power, distance and pattern together.
Exposure = power, frequency, distance, direction. If a choice lists only one factor, look for the all-of-the-above.