It's not just where they impact. You need to look at the angle they enter the target. If they are not entering at an angle similar to the fletched shafts, then you need to experiment with spine adjustments. If they are all entering the target straight in, then maybe spine isn't off that much. I've shot weak bareshafts that fly almost sideways on the way to the target.

If your fletched shaft's spine is off a mile, then it will not hit where it should either. You may want to cut off an inch or two on one of the fletched shafts and then retest. Just don't cut off more than where you expect it to end up. Your archery program should be able to help you with that. I always try to use a shaft that I expect to be a bit weak at full length to start with and then cut it down until it flys perfect. Too many people want to shoot the shortest shaft they can, regardless what it does to spine. I don't care if mine are 32" long. I shoot them at the length that gives me the correct spine.

I'm fortunate. The shop I go to, has all it's popular shafts available to test, cut to different lengths (1/2" increments). They're available bareshaft and fletched. I'm able to grab several different tip weights in the range I want to shoot and try them on several different bareshaft arrows, compared to several differnt length fletched shafts. After having done this many times, I know approximately what I'm going to need. For someone, who is doing this for the first time with a particular shaft, it may take a bit of experimenting.