Different villager type mobs (illagers, witches, villagers, etc) have inconsistent sitting poses when riding another entity

Steps to Reproduce:

1. Summon the following mobs

   /summon armor_stand ~ ~ ~ {Invulnerable:1b,Invisible:1b,Passengers:[{id:"minecraft:villager"}]}
   

   /summon armor_stand ~ ~ ~ {Invulnerable:1b,Invisible:1b,Passengers:[{id:"minecraft:vindicator"}]}
   

Expected & Observed Results:

- The vindicator will be sitting, whereas the villager will be appear to be standing.
- Both mobs would have the same sitting pose when riding an entity.

Screenshots/Videos:

1.14.4:

24w07a:
^{(Different behavior than when originally triaged)}

Notes:

1. As of 23w31a, witches no longer sink into the entity they are riding, but instead stand on top of the entity like villagers.
2. This has been updated to include the most up to date information on the sitting positions, poses, and hitboxes of the various villager type mobs, and may not 100% reflect the original issue when triaged anymore.

Mob Table:

= Does sit
= Does not sit

Mob	Pose
Villager
Wandering Trader
Witch
Illusioner
Pillager
Vindicator
Evoker

Old Description:

Pillagers, Evokers, Vindicators, and Illusioners sink down and splay their legs (like the player, skeletons, zombies, etc)
Witches sink down but do not splay their legs
Villagers and Wandering Traders stand, neither splaying their legs nor sinking down
Happens when they're summoned riding another entity or pushed into a minecart or boat