Didn't work that way.
The round had a spinning detonator inside it. The rifling bore of the gun itself spun the round, and the core would rotate with it. When the round decelerated suddenly (upon impact) the core flung forward and 2 contacts (of whatever) met and detonated the explosives.
This is a round with a slow enough muzzle velocity that it's not going to overpenetrate ANYthing.
So barring that, it's a hand grenade. Nothing more. Put a grenade in an open space, and do LESS damage. Put a grenade in a small space, and blow the living daylights out of it. The same explosion in a smaller, confined, space, will do more damage. That's just physics. Not to mention fighters were crammed in almost every inch of their wings, fuselage, tail, nose, with vital components. Bombers had a lot more space where there were no vital components (unless you count gunners?). 30mm will do more damage to a fighter than a bomber because of these reasons.