Though your choice of arrows could be the culprit I have a feeling it may be something else. For example, do you start your practicing by shooting at 15-25 yards and then move out farther? If that is the case then fatigue from shooting could be a factor in your accuracy. Second, it could just be that you need to practice more often at the longer distances. What most folks will tell you is that if you can practice at 40 or 50 yard targets regularly then 20 yards become a chip shot. It is entirely natural for group size to increase slightly as you move out to farther distances if for no other reason than because of the size of the area that your aiming point (fiber optic pin) occupies on the face of the target. As you get farther away that aiming point covers up more space and thus it becomes more difficult for you to put together as tight of a group as you would like.

Now, after having discounted some of the issues related to you as an archer it may also be specifically related to your equipment. You can try " easy adjustments" such as changing point weight to see if it is a spine issue or you can play around with your rest position, etc.. to see if you are getting some fletching contact.

Hope this helps some.