From: Melbourne, Australia
Basiically the number of contacts is irrelevant. The maximum (available) number of flights will launch on detection of a contact at the relevant distance snd certainty level specified in the mission. It's a binary--on or off--event, not related to how many contacts. The only criteria considered is 'if a contact is present'.
Whicker is right, in the example you describe a maximum of three flights will launch (the maximum number will always be launched if there are ready aircraft to meet the max; the only time you will have less than the maximum is if aircraft are readying).
The only amplification I have there is that aircraft on an intercept will move to engage the nearest contact, once that contact is no longer targetted (dead, no longer detected, turned out to be friendly/neutral) they will look for other nearby contacts before going home. If a contact meets the engagement critera of certainty level and is within a reasonable prosecution range they will be engaged. This continues until the aircraft go winchester, bingo, or run out of contacts to investigate.
There needs to be a certain level of simplicity in the tactical AI; when we start hard coding for every situation we dig ourselves into a hole that we will never code our way out of. The design principle behind the intercept AI--as well as the rest of the sim--is to give players and designers simple but powerful tools to achieve desired behaviour.
Some scenarios included with CMO that you could look at for examples of how to set up air defenses are: Pyropolitis 1-14, Operation Lightning Strike, Operation Brass Drum, Khark Island Raid, and North Pacific Shootout.