Types within a sign

Hi all. I'm totally new to Chinese Astrology. In some books my wife is defined as being an Earth Monkey (30 Jan 1968 to 16 Feb 1969), but several people including myself agree that she actually sounds much more like a fire monkey by their description.
I assume that astrologers like this one draw their specific type descriptions from broader definitions. What's the standard explanation for variations like this situation?

Category: Chinese Astrology

Hi, Ask! You know, the problem is that there is no system in chinese loonar calendar at all! They add several small months to make the loonar year the same duration as our. So your wife can Fire Monkey as well as Earth monkey.