A vehicle with real reflections in the mirrors is always more appreciated than one without.
Unfortunately, only LODs will be reflected, in other words, only the landscape, not scenery objects or other vehicles.
Don't forget to do these steps on the inside mirror too, not just the outside ones.
I'd like to point out that the point of origin on Zmodeler must be set correctly. behind (side without the mirror) the rearview mirror, not in front of it or at its level, otherwise you'll never get a visual of the rear end in it.
If you're not satisfied with the reflection, try moving the point of origin further away or closer to the mirror, but always without stick it! It's always possible to modify the reflection after testing the vehicle in game.