Sighting Question

[low_bidder]

"Once the target unit is spotted rules you guys talk about shouldnt play any role."

In SP "spotted" means you are calling arty on it. It doesn't mean 'seen' or that you can see it, although you do have to see it to be able to spot it. If that isn't clear, then join the club.
Meanwhile, I think the question was why can't you 'see' a target when you have LOS to it? Or at least that is the question I was answering. Having LOS to a hex doesn't mean you see any enemy units in that hex. Sometimes you can see 1 of them and not others.Target size and suppression can produce a nasty surprise sometimes.
One thing you can do is 'z' key the hex you suspect holds the unit firing at you. It's best to do so from a different unit. Sometimes that 'z' key will get enough suppression on the shooter to have it suddenly appear. Then you can service it in a normal manner.