Editing Warhammer 40,000/Tactics/Kill Team(8E) Guide and FAQ (section)

==Being in LoS and being obscured==
Model A counts as being in Line of Sight of model B as long as a straight line can be drawn from '''any''' part of model A to '''any''' part of model B. As such model A is also in LoS of model B. Yes this means that you can draw LoS from the barrel of a gun, which sticking out of a window, to an antenna sticking out behind a solid wall.

Model B counts as obscured for model A, if anything, terrain or other models, blocks LoS to a part of the body, head, arms, or legs, even partially. The base or antenna/flags/guns/etc. not being fully visible does not give obscured to the model. This means that it is possible for model B to be obscured for model A, while model A is not obscured for model B.

It is very easy for a model to gain the benefit of being obscured, while being out of LoS is more of a challenge.

===I don't like this and want to apply obscured conditions to determining LoS===
You can, if you talk about it with your opponent first, but accept them saying no. Having to draw LoS from the body and limbs, or even worse, just the head, has a significient aspect on positioning and greatly reduces the possibilities for a model to get clear LoS on an enemy model. For example, a model standing behind a window with its gun poking out would normally get clear shots on models standing on the open street below. With the above changes to determining LoS, those models will nearly always gain obscured, if they are even visible to the model in the first place. Instead of poking the gun out, placing the model with its back towards the window may create better LoS condition now.

While a flagpole shooting at a spike might not feel right, consider that the game and its rules are an abstraction of the battle taking place. The models are static in the shooting phase, but they would be poking around corners, or took their shot when the enemy rushed from cover to cover during the movement phase. The antenna sticking out behind the wall does give your models position away, even if it was cowering unmoving behind it. Maybe the weaponry employed is strong enough to blast through the wall, or the enemy found a gap in it. This is what the -1 to hit and to the injury roll represents.