Have you shot them bare shaft? My first thought would be more weight on the tip. that is a short arrow and your bow weight is at the bottom of the spine range. That would make me think stiff. A heavier point will weaken the shaft. I would recommend taking the fletching off of one and shooting it with the group. If it flies to the right of the group the shaft is weak and needs a lighter point. If it flies to the left it is stiff and needs a heavier point. Others will give you more detailed info, but that would be a start.