Clearly i should have added more words as I thought it was obvious I was just comparing projectile vs target; ie, just because an object is small or light doesn't mean it can't cause significant damage, and we don't have a lot of research into it.

If it penetrates the wing, can it hit the fuel tank?

And 6lb of metal hits different than 6lb of goose, depending on what it hits. Hail can destroy a radome.

Fuel tanks are kevlar-lined nowadays, no? Certainly that doesn't make them invulnerable, but they can take quite a beating before they start leaking or worse.