[When does a character not have line of sight.]

Can someone please show me examples where a unit would not have line of sight. 

I'm having a hard time figuring out when someone doesn't have line of sight. 

I'm assuming that if two characters were on the same level and there is blockable terrain that is over height 2; that would be considered out of line of sight. If they can't trace a line from base edge to base edge. 

But once you put a character at a different level. It's now considered in line of sight. I'm I correct here.

[Scenerio scoring vs rules reference.]

Only one of the 4 scenarios talk about scoring mission points for half destroyed ships. 

But in the rules reference it states you score on half destroyed. It also states scenerios change how scoring works. 

It bot clear i there is only one scenerio that scores with half points or do all 4 score on half points.