Dark Harvest is not "harvesting" on long range kills
This can be coded relatively simply... Currently is seems that a Soul only appears if you are within a certain radius. Killing the unit in question automatically absorbs the soul, else, you'll need to walk close to it.
Champs like Jhin/Xerath/Karthus/etc get no credit for long range kills however. You can't even walk over to get the soul since it never spawns.
I know this was likely overlooked since DH is pretty awful on Xerath, but it's not the worst thing on Jhin, so it would be nice to have the option to take this... considering both jhin and DH aren't currently considered "meta".