Since Guinsoo's pen passives don't stack, a suggestion

Since Guinsoo's pen passives don't stack with last whisper or void staff, may riot could double the amount of penetration per level. Getting to late game doesn't always happen and even if it does, that'd only be 9% more of each form of penetration or 24% of each. That seems a little better than 15% if you can't stack it with the other forms of percentage pen.