2% means 5 attacks for additional 10%. Thats pretty ok. It could also be done by counting done frost damage (Including spell damage). Something like for every xx applied frost damage this relict has 10% more amp to a maximum of xx.
That requires you to play a perfect game and why is there a cap that you will never reach. 2% per frost attack is barely anything unless you are able to spam cheap champs with attack frost. Spoiler you can't
