Item on Off-Hand has a different position when compared to Main Hand in First person, this is very noticeable while you holding a sword on main hand and off-hand (using /replaceitem commands), the position isn't consistent as some item will have a much higher position (like swords) while the other will have much lower position (like totem)

Step to Reproduce:
1. Get a sword and hold it in your Main Hand
2. Paste this command: /replaceitem entity @s slot.weapon.offhand 0 diamond_sword
3. Now compare it, notice that the item position in Off-Hand is much higher (or lower) than the Main Hand

Expected Result:
Both Off-Hand and Main Hand items uses the same position

Observed Result:
Off-Hand items has a different position and isn't same as the Main Hand one