Shipping costs advanced calculation

I’d like to create a specific shipping costs entity for a specific customer group.
The shipping costs should be based on a calculation, which calculates shipping costs with the formula:
€ 100 - (total order value * 0.05).

  • How do I enter this as a formula in the calculation field under advanced configuration?
  • Is it enough to change ‚calculate dispatch cotst based on‘ to ‚calculation‘ to activate the entered calculation to calculate shipping costs for the customer group selected in the so called dropdown field?