I think I'm missing something. I get the feeling that iTT does not consider the individual outputs of the groups? IOW, if you had two groups set to 0 "compensation", the shot would be one stop overexposed?
I always assumed it was calculating based on each group illuminating the same subject whether it was or not. It doesn't make sense that the exposure is set for each group independently. With 3 groups, you could be as much as 1.58 stops over.
Scott Chapin Powder Springs, GA, USA Nikonians Team Member