I thought that the way it works is that when you get a mastery, your coin reward is increased by your HP as a percent. If the reward is 50 coins and you master it with 100 hp, your reward is increased by 100% -- 50 + (50*1). If you get a mastery with 120 HP your reward is increased by 120% -- 50 + (50 *1.2) = 110.
Is this information incorrect?