Healing Booster has doubled effect on Graves' Jar of the Dead T1 heal.

[Theatre]

The T1 heals by 5 per "death" pickup, and healing booster by itself increases that to 7 instead of 6, and this holds up as the numbers get bigger, e.g. 27 is increased to 38 (approximately 40% increase instead of 20%). This also goes for Tempo (boosts by 50% instead of 25%).