Hoglin's height is 1.75, pivot at coordinates (0,1,0), but the hitbox is calculated around pivot, then you can calculate 1.75/2=0.875 < 1, so you can't hit the hoglin by throwing a projectile from the bottom of its foot.

I created a behavior pack and change the pivot, it can fix the bug.

How to reproduce:

Use a projectile to shoot hoglin's feet.

Observed Results:
Sometimes you can't hit hoglin.

Expected Results:

All projectiles should hit hoglin.