I wanted to test out the mechanics of SM to see if it costs mana to switch targets, and this is what I did.
Smacked on target dummy naked while monitoring overhealing.
45 ticks of soothing mist interrupted ASAP.
50 seconds
@63% mana
45 ticks uninterrupted
50 seconds
@75% mana
81 ticks interrupted about half way
2 min 09 seconds
@62 % mana
81 ticks uninterrupted
2 min 09 seconds
@71 % mana
(9 casts = 81 tick. If you consider twice as many initialed SM casts, that is an additional 9 casts at 3k mana each. 9 *3k = 27k. 27k/300k = 9% more mana consumed, which is what you see above.)
So yah, my guess is you are paying 3k mana upfront for that next SM tick.
Is there a flaw to my test? Can anyone else confirm/deny the results?