Dart brake issue

It could be the MC is too small in bore. A smaller bore will give the soft feeling. Too large will be a lot harder to push. The brake require a certain pressure to work. You have you foot to create that input pressure, multiple by the MC bore. Too large of bore, requires more input pressure, too small the pressure builds to max quickly and require less input of your foot, making it feel soft. It boils down to what is your personal feelings as to what foot pressure you are looking for.