The Bug

Ghasts are only affected by splash potions when it hits their lower half. Even if the potion hits the top half of their hitbox, it does not affect them and the potion splashes nonetheless.

How to Reproduce

1. Summon a ghast with no AI using the command: /summon ghast ~ ~ ~ {NoAI:1b}
2. Get any splash potion (preferably one like poison or harming so that it is easy to tell if the potion affects the ghast or not).
3. Splash the potion on the bottom half of the ghast's hitbox (not the tentacles). Note how the potion affects the ghast.
4. Splash the potion on the top half of the ghast's hitbox. Note how the potion does NOT affect the ghast.

Expected Result

Ghasts should be affected by potions no matter where on their hitbox the potion lands.