I'm guessing that's where the bolts don't bury to the fletching. The foam insert may work for verts but..... Just had such an experience. Reworked a off brand foam target over the winter to tighten the layers. When I tried it the first time (at 15 yards) the arrow passed through the target, the mud flap backing and into the 3/8'' plywood behind that. Took some grunting to remove it!