I too have seen inconsistency with the sunny 16 rule in South Georgia. It's mainly sunny 11 dropping to 8. I just attributed it to varying levels of hazyness; humidty, pollen, and polution along with composition. There have been many times when I thought the meter was underestimating the amout of light on a seemingly sunny day but in most cases the meters were right and my eyes were wrong. Gotta get better at reading the shadows and color lightness I guess.