Going by a percentage of OSA in my estimation is a bad way to determine the correct amount of ventalation. I prefer to let the OSA air "float". That is to say CO2 controlled ventilation which varies the outdoor air supply in response to CO2 which is used as an indicator of occupancy. CO2 controls may be useful for reducing energy use for general meeting rooms, studios, theaters, educational facilities, etc., where occupancy is highly variable, and irregular.
A typical system will increase outdoor air when CO2 levels rise to 600-800 PPM to insure that maximum levels do not exceed 1,000 PPM. The system should incorporate a minimum outside air setting to dilute building related contaminants during low occupancy periods. A drawback is that CO2 sensors must be calibrated periodically and setpoints may need to be adjusted based on outdoor CO2 levels around the building.