Okay, so I did a search and could not find this particularly, but I had a problem with my last game against a Tau player and either I don't have a clear understanding of the cover rules(entirely possible, been a whole year since my last game) or he was trying to pull a fast one on me. The entry for the Tau smart missile system says that it may be fired at targets without the need for line of sight. Does this mean that it can shoot at targets further than 6" into terrain? I said no, he said yes, then tried to justify the smart missiles going around to another side of the cover my unit was not 6" from and said the missiles went "around". 
I think I may be shaky on this, but then again when time was up at the FLGS(end of turn two) with my Flyrant, 3 flying ripper bases, 18 hormagaunts, 4 hth warriors and a small handfull of genestealers in combat with his only commander and bodyguard(no other crisis suits) and all of his firewarriors with the rest of his army within consolidation distance(his 6 broadsides within 12 inches of eachother, everything else dead) he insisted he won anyway, by victory points. Yeah kid, you won.