Multi Target Damage Reduction Mechanic Idea

So the idea for this multi target damage reduction mechanic would be a new way for damage to hit multiple targets while only doing a set amount of damage. as we all know most skill shots that can pass through multiple targets tend to have penalties for each target hit (Zed Q, Ezreal Ult,Caitlyn Q ect) resulting in up to 70% of the damage being removed. Now the idea that I had for another form of damage reduction would be to have the ability always do a set amount of damage after all targets have been hit, for example if there are three minions in a row each having 100 health remaining and the ability's damage is 260 damage and the ability is fired to hit all three minions the first two minions would absorb 200 of said damage and the third would only take 60 damage. This "set damage" can be reduced by armor/magic resist but will not reduce the total damage dealt. So in the example of the three minions all at 100 health if they all have 10 armor/magic resist (BTW i do not know how RIOT does their damage reduction so we will just assume that 10 armor/magic resist results in 10 of the appropriate damage being avoided) the first two minions would absorb 110 damage each, resulting in the third minion only receiving 40 damage. In theory this ability could pass through as many targets as can fit within its range provided that it deals enough damage to kill of the targets in said trajectory.

While i do realize that this is a little bit of a strange concept i think it would interesting. As for the actual reduction in damage done to the minions try to think of the armor/magic resist as "Phantom Health" so while not actually having 110 health each, for calculation purposes to treat the minions as actually having said ammount of health.