As you probably already know TLoS (True Line of Sight) is one of the many mechanics changes in the new 5th edition of Warhammer 40K. The confusion that this is causing is mind numbing. I didn't realize that so many people would be unable to grasp the simple and literal fact - if you can see it, you can shoot it.
To clarify any debate I've posted an excerpt from the actual rulebook.
"Line of sight literally represents your warriors’ view of the enemy " "Line of sight must be traced from the eyes of the firing model to any part of the body of at least one of the models in the target unit (for ‘body’ we mean its head, torso, legs and arms). Sometimes, all that may be visible of a model is a weapon, an antenna, a banner or some other ornament he is wearing or carrying (including its wings and tail, even though they are technically part of its body). In these cases, the model is not visible. These rules are intended to ensure that models don’t get penalised for having impressive standards, blades, guns, majestic wings, etc." "Firing models can always draw line of sight through members of their own unit"
Furthermore let me state that AT (Area Terrain) poses ZERO effect on TLoS and only now pertains to cover saves and difficult terrain movement.