What if the amount Sanctuary heals is reduced based on the number you have in play?
1 -- 4 hp = 4 hp
2 -- 4 hp, 3 hp = 7 hp
3 -- 4 hp, 3 hp, 2 hp = 9 hp
4 -- 4 hp, 3 hp, 2 hp, 2 hp = 11 hp
5 -- 4 hp, 3 hp, 2 hp, 2 hp, 1 hp = 12 hp
6 -- 4 hp, 3 hp, 2 hp, 2 hp, 1 hp, 1 hp = 13 hp
The coding would be simple and the text could be changed to: 'Heal up to 4 HP per turn.'