If the intent of this perk is not to be a last minute full heal for when it all hits the fan, how about it restoring direct HP (red HP) based on a % of the kill, so long as you are in the AoE, along the armor restore boost?

So say for example player 1 kills an enemy by dealing 10 damage. Each player gets healed for 2.5 hp assuming all 4 are in the AoE. Obviously scaled in a balanced way. When you can be as granular as you want, the sky is the limit, right?

That way we avoid it being a last minute button, a full heal that honestly has felt extremely situational, and it forces the party to stay with the tank.