"Shelling" effect not working on bosses?

[JohnnyTheWolf]

Before the fight with Big Shiee, I picked the "Shelling" mod for Marco's machine gun. However, when targeting Big Shiee with it for a team sync attack, I am told that Marco's machine gun only inflicts 6 points of damage.

Is this a bug or does a vehicle like Big Shiee not count as a... vehicle?

[С Г エ χ]

I'm not sure if it's a bug or balancing issue, but you DO fight non-boss vehicles on the other difficulties