What determines the effectiveness score?

I'm confused why the score is so low, while the ordinary score is high when they have all the same main ingredients. In fact, on your comparison list they are identical for at least the first half of the list, while the majority of the rest are the same as well, only appearing in a different order. Why would the ingredients toward the bottom of the list, meaning they are the least ingredients in the formula, have such a big impact on the score?