I would rather see mastery being divided by how many targets a spell affects, so for Vivify, 1/3 of the mastery healing can be applied to every person healed and for EF 1/18th per hit (or even better have master proc three times over the 3 secs and each bolt gets 1/6th of the benefit). Soothing Mist should definitely proc mastery every X/sec (or a small percentage of Mastery at every proc). Overall, I think it would be better if mastery directly impacts all spells instead of only some of them and only on one target at a time. Healing numbers and the power of mastery would have to adjusted accordingly of course but such a change would make mastery more consistent and useful in all situations.