http://www.sc2replayed.com/replays/63611-1v1-terran-protoss-kulas-ravine
This is a game I had earlier tonight on Kulas Ravine where I had the high ground by Terrans base which he was unable to get to because of rocks. My understanding is if you don't have an air unit or a unit on the ramp you can't see the units attacking you. However, after watching the replay, once my stalkers engaged the siege tanks on the lower ground they became visible to the Terran player and he was able to hit them with his siege tanks. He didn't have any air units gaining him line of sight or access to the ramp because of the rocks. He was even able to reach my colossus that was at max range with the range upgrade that was also on the high ground. An orbital command scan wasn't used either.
My question is how was he able to see my stalkers and attack them without gaining line of sight? My understanding of how that works seems to be incorrect.
Best Answer
So your understanding of Sight and Line of Sight is correct, without any unit up there there is no way he can see or target your stalkers (even if you attack him, which was not true in SC1), unless he:
Looking over the replay he does scan you at 14:08 to attack your stalkers at the high ground. At 12:16 he gains vision of your Colossus because it counts as an Air unit for purposes of vision.