Right now, there are two options for mission expansion: on and off. And while mission expansion is a great feature that makes the game more fun and realistic, but I think a new option could be added to make it less frequent. There could be an option for mission expansion on 25% or 15% of calls, for example. Another similar feature could be added to fire alarm calls, where we can adjust the probability of them becoming real or a false alarm.
I think these options would be a great addition for premium account members, IMO premium accounts should get more features.