If you are over draining and need a higher setting, you are not going to ever make enough csf to raise the pressure (visualize over draining, you can't catch up without slowing the draining, aka raising the opening pressure on the valve!!). A person makes about the same amount of csf daily (avg adult makes bit over 500ml/day, completely replaces csf in use more than 3x a day). Yes, people can take a while to adjust to new settings but that's more a factor of compliance, my daughter takes longer than many but if the setting is too high, we figure that out quickly. Your surgeon is being careful but maybe too careful given the details, two notches should be ok or less time between adjustments. It sounds like you need to ask what the plan is if your right setting is anywhere above 20cm. My daughter's pressure issues are probably not the same situation as yours as she is still a growing child shunted as a baby and did not have any obstructions in her ventricles. Kids' pressures change as they grow and most don't need lots of adjustments, those who do need adjustments usually stabilize by 8-12yo.