In the first attached screenshot, note that the guy with the tower shield is somehow not regarded as obscuring the target (the wavering raider with a pierced hand). From what I’ve seen, this occurs whenever there is an equal number of hex-lines between the shooter and the target from both the front and the side (e.g. two lines between them straight ahead, and also two lines between them to the side, as in this example).
In the second attached screenshot, the shaman is surrounded by a grey boulder (to the left), some yellow dense-shrubbery (directly ahead) and some red/brown dense-shrubbery (to the right). Somehow, however, the thrower is able to target it. If the shaman was immediately behind the grey boulder (on a line immediately to one side of the thrower), it would definitely not be targetable. Yet, because it’s one line further to the side (but fully enclosed by other sight-blocking objects), it’s miraculously targetable.