Error enchantment efficiency on tools

Hello,

I have a problem with the enchantment efficiency on the tools, for example I have a basic very efficient modded pick, more efficient than diamond, it works well but when I add efficiency 5 for example on the modded pick and the diamond one this one have the same power and efficiency while my modded pick is supposed to be faster because it is faster when there is no enchantment, would you know why?

Thank you in advance!