Game Design concept (feature) for smiting champs!

I just was thinking that for smiting champions it would be a good idea to make the smite do less and less damage as the enemy champions hp gets lower and lower. I feel like so many players will be using a ability like this to secure (steal!) kills. If the ability was made as a polar opposite of execute ults like Rivens and Garens this would help a lot. Example is the jungler comes charging in to give his gank and has the enchantment that causes his smite to slow, there is utility and idea in a change like this! If anyone has any feedback they could give me I'd love to hear how this could be changed or improved. If it is not do able please explain why. I am curious and seeking further wisedom! :) If someone wishes for me to elaborate my thinking I shall at request.

  I love being all deductive sometimes and this should be interesting! :D