"Let's assume that there were several sighting shots, and that they got closer to the target. Wouldn't the target therefore know that he was under fire, and consequently be unlikely to hold still in an exposed location for nearly 10 seconds?"
Not neccessarily. I dimly remember bits from basic training about stuff like this (but it's been 30 years now), and off the top of my head:
1. You might not even notice a couple of incoming shots around you, depending on what they hit and how buisy you are. Especially if they come from far away and the sound, even if you actually hear it, doesn't match the timing of noise/impact you are familiar with.
2. Let's say you notice and recognize the sighting shots for what they are - but you can't tell where they are coming from. All you know is that there is a sniper somewhere who's really far away. So for all you know, shifting your position might make it easier for the sniper to hit you. At the sime time you know that you are relatively hard to hit where you are right now due to the distance. I guess I'd toss a coin.
3. Let's say you notice the shots - and conclude that someone wants to drive you away from your position. Maybe to lure you into the range of, say a mortar or something like that.