Is that even possible? You can't have "40% chance of 5* with only the 3 listed tanks in that 5* group" when one of those "3 listed tanks in that 5* group" is a FOUR star tank...
I'm pretty sure it's 40% chance for ANY soviet 5 star tank (which includes Yuliya, IS-3, IS-7, and Centurion, among others). IIRC that's what a developer said on Discord too but I don't remember his exact words.
40% of getting "the three listed 5* tanks" can't be right considering that one of those listed tanks isn't a five star tank yet it says "40% chance of a five-star tank".