Nowadays all aircrafts with lock on missiles can lock targets on distances more than 3 km if your overall view distance (in game settings) is set to more than 3km. But AA vehicle cannot do that. AA vehicles are too weak against aircrafts with Lock On missiles and couldn't shoot back or survive against this kind of weapons.
Aircrafts of any kind should be afraid of AA vehicles but nowadays they don't.
Please provide AA vehicles with more powerfull radar systems, IMO 6-8 kilometers is ok.