Block chance math

Good afternoon,

Let me start by saying you all have done amazing job with path of exile 2.

I have 3 characters at lvl 70+ and have not run into mathematical errors. That said the way block chance works after taking the turtle charm seems broken.

I have a 25% block shield equipped and recently acquired a 40% block chance shield and the extra 15% did nothing for my block chance.

If this is not an error can you inform hos the math works for block after taking the turtle shell passive.

Thank again for a great game