[ARAM] Soraka Heal is not healing for amount noted on tooltip

I randomed Soraka in an ARAM (I know, how lucky). I noticed that my heals felt lacklust. I started testing it in game and the value healed when cast on an ally was not what was specified in the tooltip.

I confirmed this problem when I had rank 5 of my heal, a deathcap as one of my items, and was healing an allied Zyra with no other debuffs on her.

The base heal was 240 (+222 AP) but the heal was only for around ~240.