Straight from Castle Age!
Cleric Heal Adjustment
We have made an adjustment to the Cleric Heal Abilities. Similarly to how polymorph gets a reduced challenge to successfully polymorph a target, the Cleric Heal ability will as well with the following difficulty reduction:
Heal I - 5% Easier to Major Heal Target
Heal II - 15% Easier to Major Heal Target
Heal III - 25% Easier to Major Heal Target