Limitation of impurities in ICHQ3B

Hello and I hope you are doing well
I want to ask you some questions about the ICHQ3B.
At first, I want to know more about the limitation of impurities. The limit of Fulvestrant sulphone in USP monograph is 1%, and there is not any limitation mentioned for beta isomer and both of them are specified impurities.
In ICH Q3B, if the maximum of daily those is more than 10 mg, the threshold for identified impurity is 0/2%.
Which of the limitation should be accepted for Fulvestrant?
How we can calculate the maximum daily dose for this drug?
I will be so glad if you give me some information to understand this limitation of impurities about Fulvestrant.