best temperature range for my incubator!!

Hi guys. Im from India. I build an incubator which is a semi forced air type (the pc fan works only when the heating element is on). So it probably won't have same temperature every corner all the time. The reason I'm here for I want to know the best temperature range for these kind of incubator (high and low, the difference should be 2 degree Celsius) . I searched Internet for it but everywhere I get different opinions. I know 99.5f is best chicken incubation. But what about semi forced air /still air incubation? Please anyone reply..