>hidden mechanic
>Counter intuitive
>Makes negative sense
>Need a spreadsheet, wiki and mods to calculater.

Arrowhead, more like retardhead.
they should just make it 'pierce' and 'shred' damage; and 2 hp bars, 'hard' for most bodyparts and weakspots, and 'fleshy' for bulky monsters.
A bodypart can only have 1 hp bar. 'shred' dmg is done by the likes of hollow point or shotguns. Some weapons, that pierce and Then explode, do both.
The 'shred' of a shotgun wont go deep in a weakspot (like a control unit or brain), hence it does less dmg. likewise a piercing projectile doesnt shred the meat of Fleshy enemies who arent much affected by bleeding and vital organs (like flesh mobs). This dmg reduction (shred dmg vs hard hp bar and pierce dmg vs fleshy hp bar) ehould be 80%.

Note: i have never played that game. I pirated both helldivers 1 n 2 but it didnt open on my pc.