They have a built in 20% attack boost (buff) because they are controlled by the AI (Artificial Intelligence) which is not that intelligent. So all their attacks are, on average, 120% of what is stated (x1.2) so a 345% attack becomes a 414% attack. They can also be weaker or more powerful using mathematics that only SG knows. Edit: as @baga points out, this boost in power applies to their defense also.
Hope this clears things up a bit.