Enter editor. Create yourself as anything Blufor. Do this on, say, the Stratis airfield runway. (for greatest visibility)
Beside you, create one Rifleman [AT], should be under your command by default. If not, place him under your command.
Create one Ifrit vehicle around 400 meters from you. (no more than 600...I think the NLAW has a max range of 600) make is the standard without guns or grenade launchers. No need to be dodging bullets while we're experimenting. Also, giving a car 0 ammunition doesn't seem to work either but that's another issue
preview. command your guy to attack the car. he should use his NLAW but he doesn't he only uses his rifle. I believe at this range he should be using a rocket to take out an enemy vehicle.