One thing I do (and advise others to do if they are going to use how the arrow looks in the target) is to shoot fletched shafts into the target from your farthest comfortable distance. Unless the tuning is really bad, the fletching will do its job and the arrows will enter the target straight. Now if these fletched shafts look straight the target might be ok to use to judge tuning. If they show nock high, nock low, nock right, or nock left entry, the target is most likely changing the arrows entry and the target should not be used to judge tuning.