LoS and obstructed issues are obviously a problem in this game. In a perfect world, we should be able to visually tell whether the opponent is in LoS, but we cannot always account for buggy terrain or environmental objects.
I suggest a more explicit way to visually let the player know the opponent is not within LoS by shading the character model gray (perhaps not due to dyes) or by some other distinguishing graphical way.
Only do this for LoS and obstructed, not for out of range.