Creating a distinction between heals and shields

Right now, shielding and healing are not very distinct from each other, except that shields are more or less strictly better than heals. You can pre-emptively shield somebody to bring them above their max health and in a scenario where the target has already taken damage, if the target doesn't instantly die, a shield is effectively a heal, except in some edge cases, damage over time effects and things like that. But what if shields were made more distinct from heals as a support tool? What if shields had lower base numbers, but they shielded for a percentage of your current health in addition to those base numbers?