I haven't tried the NC Sparrow yet, but the Starfire locks onto the target as soon as you place the reticule over it. That's why slow or stationary targets are so easy to kill.
MAX units are slow to turn, so use that to your advantage. Make it hard for them to track you and you're one step closer to being a better pilot. When TR or VS AA MAXs open up on you, duck behind cover so the VS lose lock on and the TR can't hit what they can't see. Against the NC Sparrow, try and limit how long you stay in their sight. The less time they maintain lock on, the fewer missiles you'll have chasing you down.
Of course I shouldn't be saying any of this. Potentially fewer kills for me if you pilots get better.