Soraka's Astral Infusion (heal) uses % HP. Why not return % as well?

https://i.gyazo.com/1fd6d86fef8805894d1af0736e476f18.png

Early game her sustain is pretty good, but if she doesn't have much AP (typical for supports) then come late game she can't even budge her tank's health bar. I suggest dropping a little of her flat heal numbers or AP ratio and give the heal some % bonus, so that it works a little better late game.

An alternate suggestion would be to decrease the % HP cost as she puts points into it, or gains levels. 10% HP hurts more and more as she gets items she may be expected to get as a Support, such as Sightstone and Locket.