When creating a new subzone, the numbers in the boundary zone are not used, so we have to re-enter those number again. Would it be possible that the number in the boundary zone appear in the new subzone created?
You don't need to renter the settings from the boundary into the subzone. You only need to enter numbers that are different to the boundary. That's how subzones work.
Eg if the boundary max slope is 1% and the subzone max slope is unticked then 1% would apply. When you click calculate, for each design parameter (eg max slope) OSD starts at the highest priority subzone and works down to the lowest. If it sees a value applied (ticked on) it uses that and ignores all values in zones with lower priority. Boundary zone is always lowest priority.