About artillery - When setting up your missions you want your FO or HQ to be able to see as much of the target as possible. For example, when calling in a Linear mission you don't want only to see both ends of the line, you want to see most of it's length. And, most importantly, you wan't to be able as much of the surrounding area too, as has been mentioned in other threads.
It can be frustrating, when spotting rounds go astray, e.g. land off map, in thick woodland, or even behind your spotter. But, that is a fair reflection of spotting problems in WW2, just cancel the mission, and move your FO or HQ to a better position.