Ghast fireballs should deal 6 projectile damage regardless of difficulty level when they hit a mob directly.

Steps to reproduce

1. Give yourself 2 leather caps.
2. Enchant one cap with projectile protection.
3. Give yourself high level health boost and instant health effects so you have lots of hearts.
4. Make a ghast containment cage of some kind and summon/teleport a ghast inside of it.
5. Switch to survival.
6. Let the ghast shoot you while you wear each cap.

Expected result

You take less damage wearing the projectile protection cap when fireballs hit you directly. (Note that if you start to take non-damaging hits, that is a separate bug that can be worked around by changing position slightly between shots: see MCPE-78714) .

Observed result

You take the same damage from direct hits wearing each cap.

Code analysis

The projectile component in fireball.json has no impact_damage section within the on_hit parameter. Compare this to the small_fireball.json, which correctly gives blaze fireballs 5 projectile damage.