[Imp]

Maybe you have found a bug setting armpr engagement range to zero, it should not engage anything but has a minimum fire range of 2. Might be a problem with the unit class though I dont rember my ATGMs firing at barges unless I set them to.

I would set it up as follows, standard saved setup, might adjust lower armor range for the opponent I am expecting.

255
9
35 - Milan range 40 depending on terrain but 35 or so a bit more accurate.
4 - if you let the enemy get that close may as well open up its going to get detected.
4 - as above might vary +_ 1
35 - I want it to fire at ATGM vehicles even if it misses a reaction shot could spoil its shot & save the target.

Unless they are included in formations I always buy units in the following order in defrence to game engine mechanics, prefer that than having formations with scouts etc as second unit.
Having similar units together makes setting filters simple do the formation & also makes finding simple, all AAA together makes cycle through who has a target using P & N keys fast.
Pet peeve finding FOOs in scenerios.

FOOs just for ease of finding could buy last
Squads Foot or truck
Squads Mech
If not part of company
Support weapons MGs etc
Scouts
Any additional support transport vehicles.

Tanks worst first if multiple types normaly so light and armored cars first, occasionaly if using for scouting might buy after main tanks.
ATGMs foot & vehicle
AAA normaly none radar first including MANPADs

Artillery
SEAD
Other air
Can buy after FOOs always artillery first in case you want to suppress AAA, just find it convineint as get arty percentage.

Cross attach to the respective companies and your good to go..
The game reaction fires top to bottom so setting up this way units you want to stay relayivly quite like scouts ATGMs only fire after the other units.

So vs a tank for example if a valid target firing order is
Squads
APCs
Scouts
Tanks
ATGM
AAA gun
Helicopters

Might end up wasting a bit of ammo with things like APCs firing AP with no hope but causes suppresion just in case your tank or ATGM misses giving them a better chance of surviving for a second shot.

Its purely taking advantage of the game mechanics but means you dont need to set up much.

HQ F00 range to 4 or so
Foo vehicle range reduced.
ATGM op filter
Tanks sometimes op filter.

This set up especialy if you have IFVs tanks only fire if they havent dealt with Enemy APCs & infantry so they dont get overly distracted anyway.
There are a few tanks that need micro mamaging & I would buy after ATGMs as there ammo load is critical.
Say 20 AP rounds that need point blank, rear shot or worse but have 3 effective HEAT rounds & mediocre targeting abilities.