Assist Duration Determined By Damage Done To Target

If someone does 80% damage to an enemy, and a teammate kills that enemy after the timer for acquiring an assist on that enemy has expired. It really doesn't seem fair if you don't get an assist for that kill. So I thought it would be a cool idea if, depending on the damage that you do to a enemy champion, will determine how long you will be eligible for an assist on said champion. Because doing 80% damage (just a % number), to someone who does 1% (again, just a % number) is a big deal. Just think its fair to award someone who does damage a longer time to receive an assist, rather than someone who doesn't do as much damage to the enemy.