These are much improved, but you are still going too deep. Cut them off another 1-2 inches less deep. This will help with the knees. By arching, you mean lumbar extension? (there seems to be some confusion on this board, arching to me means accentuating the normal lumbar curve, vs rounding or flexion (the mad cat position)). I agree. Brace harder (big belly breath, tighten your mid-section like someone is about to punch you in the belly). You are actually still getting flexion/rounding at the bottom, but again, cutting the depth may lessen or eliminate this.