i have been shooting the past few days using a 1 inch thick foam pad. It stopped the arrows atfor about 50 shotsbut then the arrows began going completely through. i add a couple more layers of foam and made it about 3 or 4 inches thick and after about 5 shots, the arrows began going through again.any guesses to why this may be. I am not overdrawing at all and the pad is still in good shape.