Equipping a block on your head with a head's item_model looks different to an actual mob head

Easily reproducible, just give yourself these items:

/give @s minecraft:carved_pumpkin[minecraft:item_model=ice]
/give @s minecraft:carved_pumpkin[minecraft:item_model=skeleton_skull]

Equipping the first: block on head correctly appears as ice, as expected

Equipping the second: block on head appears as a skeleton skull, but incorrectly (it looks to be shrunken and shifted downward into the player’s neck)

Equipping an actual skeleton skull: block on head correctly appears as a skeleton skull - this is how we expect the second item to look when equipped