Wouldn't the target therefore know that he was under fire,
You do some sighting shots that are close to the target but not close enough to give the game away. My uncle was an artillery major in Burma and he used to try and work out cross winds and temperatures from different heights - you cant do this when sniping but when laying wast to areas you can get enough shots in to get some feel for it apparently. I guess modern shell would tell you all you need to know just before they hit now. Wont be long before a 0.5" can do that too!