Nope op is correct, there are places were there is no line of sight and you can get attached through “solid” objects. The one I can think of is in the spider lair. The spider Queen can fire poison right through the floor of one of the ledges. Wouldn’t call it a cheat, more like a bug…
I've only noticed this in patch 9 which introduced the bug with doors that means they look closed when it's actually possible to walk through them. I've found that in this case, enemies can still shoot through the bugged door but my party actually needs to walk through it (or "open" it then, as that actually closes it, open it properly) before they can target the enemy.
Which isn't to say that it doesn't happen in other places where there isn't strictly line of sight, just that I've never noticed it. I certainly wouldn't be that surprised if there was some bugginess at the handling of line of sight especially when verticality is involved, given the latter has a number of other known issues with spells.
