Dagger 1 here, see Dusty. Also we were switching around between the final two track parts that had ended up in Bulldog's and Dagger 1's inventory, while trying to resupply the repair vehicle at the ammo vehicle to get more tracks into the repair vehicle's inventory.. unsuccessfully.
About armour. We've spent a LOT of ammo firing into Objective Camel's artillery vehicle, until Hammer told us that the camo-nets, covering the artillery, blocked our shots. (That is kind of inappropriate that they do that) So we drove around to find holes in the net, and destroyed the vehicles easily enough.
About enemy MBTs I can't say anything conclusive, other than they may just not have to blow up. Like how you in ACE can keep throwing HE at a truck, utterly destroying everything on it, but will not blow up before you throw some HEAT at it. Or how you can throw a tank AP round at a chopper only to do trivial damage, until you use HEAT, which blows it up, or HE which fucks up the rotors. This is all something I love about ACE, partly because it makes a difference between HEAT and AP that vanilla only differentiates in damage (as it appears to me).
TOPIC!: BUT I think AP normally and eventually result in cook-off when used on MBTs, but maybe it IS very dependent on where you hit. Maybe, maybe.. you can keep hitting the front, hitting crew, destroying engine, tracks, disabling turret, but never start cook-off, so you don't know when it is defeated. I don't know.
FTR; ACE does not tweak vehicle damage in any way, other than running the cook-off script if a particular vehicle part has low (or zero) hitpoints. All the vehicle part damage (gun, engine, tracks, etc.) including it "not exploding" was in the game prior to even Tanks DLC, though it was tweaked during that DLC.
Vehicles explode only when their "hitpoints" reach absolute 0, which happens rarely with modded (esp. RHS Russian) tanks due to them having higher "hitpoint" value, so you are more likely to disable a tank by damaging its parts rather than it blowing up.
HEAT rounds are not any special than AP rounds, they're all exactly the same to the engine, ... but HE/HEAT have an "indirectHit" value and a larger hit radius, so they damage more parts of the tank at once (lowering its overall "hitpoints" value more), causing it to explode with fewer shots.
Regarding targeted shots - yes, if a vehicle has an "ammo" like part defined and you damage it directly with AP (or HEAT), ACE runs the cookoff script. Vanilla prioritizes it too, but it makes the vehicle blow up, not cook off.
I'm not so sure about this. I'll have to test it again. Have you got any sources, linkable or just "tell-able", so I know where you have it from. All from exploring ACE game code? One thing is how HEAT has blown up choppers, while AP slightly damaged them (and before you argue about the explosive damage HEAT adds) and HE usually only damaged the heli overall. If true; that heavily suggests that AP is not treated like HEAT, or that they are heavily differentiated in vehicle type. I'll have to test some more, with some more samples, when I'm with my desktop PC again. Thanks for the answer Freghar.
I'd link you the configs, but configs.arma3.ru seems to be finally down, so you'd have to look them up ingame.
Basically, a CfgVehicle is considered "destroyed" (vehicle blown up, soldier dead, etc.) when the hit "parts" (limbs on a soldier, pieces of a vehicle, etc.) are damaged enough so that their weighted sum adds to 1 (they're all values from 0 - not damaged, to 1 - fully damaged). This means that you can sink insane amounts of damage to ie. the engine block, but as long as the projectiles don't penetrate further, the overall hitpoints will remain the same and the vehicle never blows up, as the engine is only one out of, ie. 15 parts, so only a "tiny" portion of a vehicle is damaged.
You can see this in Zeus when you see the "Heath" (Armor?) bar of the unit/vehicle. If you set it manually, it re-sets all hitpoints of all parts to your specified value, which is why it ie. repairs wheels magically ... because the wheel was completely destroyed before and now it gets non-0 hitpoints (well, less-than-1 "damage" value -- it's the other way around).
As for HEAT/AP differences - take a look yourself into CfgAmmo. If you want a direct reference, you'll have to inspect the CfgVehicle class of some vehicle (ie. a tank), look into its subclasses and you'll find CfgWeapon definitions somewhere as Turrets, then go into CfgWeapons and see what those weapons use as magazines, then look those up in CfgMagazines to see what CfgAmmo class they use as ammo, and then finally look into CfgAmmo to see the actual projectile properties.
You'll see that they're basically identical across ie. shells of a tank, with the only differences in indirectHit, penetration values, raw (hitpoint) damage a.k.a. "hit", etc.