An orthographic camera is used, so logically there shouldn’t be a situation where objects are larger when they are closer and smaller when they are farther away. However, when firing upwards, the blue bullet appears shorter, while it is normal when firing downwards.
This has no depth, it doesn’t look bigger when near and smaller when far. You should look at the prefab of the particles.
Yes, it is the correct effect that the objects are not larger when they are closer and smaller when they are farther away, but I have not found out what the problem is with the particles. 
If you look closely, the particle length is the same, but the smoke effect at the end covers it up.
Yes, what I don’t understand now is why different angles affect the distance from the smoke trail to the blue particle bullet.
You may have hit the bullet and 
it slowed down, so the smoke trail became shorter.
The speed was faster before, so the smoke trail was longer.
This bullet is setPosition in update, so there should be no speed decay