Yeah, but the model isn't its base. It also has a height. I might be misunderstanding you, but it sounds like you don't really take the height into account.
We play that if one or both models is of greater height than any intervening terrain, there is LoS. Ht2 - 1" - Ht1 has sight. There are certain angles where this becomes absurd. For the most part, we manage to avoid this, but in those few situations where it becomes absurd, we tend to move to more of a true LoS.