Falcon Dive works incorrect!

Before use shield which doubled my Accuracy I hade 6463 Accuracy on the skill "Fangs of frost". And with that accuracy and passive Falcon Dive I had 2.85 attacks per second. But when I use shield my Accuracy becomes 12926. It means that i gain 6463 Accuracy more. That means that I should gain approximately 25% increase attack speed.
BUT when I go ti skill info I see that my "attacks per second" is 3.19 what means only 11.5% increasing

Could somebody explain me why not 25%????