PBS Dependent Application Query from Online Form

I am planing to apply my Wife's and daughter PBS Dependent visa. My COS was generated for 5 years in 2018 and is valid from Jan 2018 and expiring 2nd Feb 2023 on BRP. Although I have 3 years valid visa still application is estimating the fees for my dependents on the basis of 5 years for both. During the application there is a question what is the length of your CoS. If i select less then 3 years i am getting 3 years standard fees for my dependents.

If any one of the experts confirm which option do i have to select it will be great help.