HEAT based ATGMs are hardcapped to either 20 or 30mm of Overpressure penetration depending on if they are tandem or not.
For HE, overpressure damage is calculated when a shell fragment from an explosion hits something inside of the vehicle, proving that explosion got inside of it. This leads to high-yield explosives nearly always taking out a vehicle in a single hit, due to the shockwave being able to move around frontal armour and to hit the entirety of the crew that way.
HEAT and HESH shells and ATGM can also create overpressure damage but are less effective at it compared to HE ammunition and seem to only affect vehicles when very thin parts of the hull or their critical weak spots are hit directly, with overall armour thickness of hit surface having to be below 15 mm RHA, since their explosive power is directed towards creating special effects (molten jet for HEAT and scabbing for HESH) instead of producing shockwaves. There are exceptions in HEAT ammunition, which can deal overpressure damage through 20 mm (select few powerful HEAT ATGM) or 30 mm RHA (most tandem missiles). Tanks with reasonable amount of armour will not take overpressure damage from HEAT, even if special effect penetrates them easily.
"This mechanic affects vehicles with thin armour negatively, but, unlike with the hullbreak, any tank is potentially vulnerable to overpressure damage. As a result, it makes not only light, but also heavy tanks easier to destroy by using bombs, rockets, big HE shells or artillery strikes. To utilize the mechanic effectively, be sure to aim for a weak spots on the armour, such as roofs, vents, bellies, tank rear and overtrack sponsons, to maximize the chance of a successful penetration.
