Sorry--at work, and can't look at the logs. However, I could offer suggestion, as Disc priest...
When the ball is about to hit the boss, hit your tank with your single target damage reduction cooldown...it's a very vulnerable time, damage-wise, as the pally healer, if working inside, with the melee, will be moving out of the way, and may not be throwing a heal, at that time. You may even consider having the pally healer (or yourself, if inside) position away from boss a little earlier than the melee...depending on your raid makeup, and number of melee, etc., of course.
Also, try to ensure that the tank uses his cooldowns, at that time, too. Sometimes that !@%#*! ball will head for the tank, or make the tank share damage with the boss...don't know if it's a bug, or just random.
It sounds like your stack phase is ok, as far as healing--I use barrier, for the first one, then Hymn, for the second, with our druid healer using AOE cooldown, on third...we have a Shammy healer, on the inside, for melee/tank healing. I use atonement spec, but, having gone through a lot of what you seem to be describing, I did try alternatives, which didn't seem to make much difference. I do recall forging more Mastery, at about that time, though. Smiting/Holy Fire worked, during ping pong phase, along with penance and PoH...penance actually saved the tank, on more than one attempt, during that last bounce before stacking, too.
Good luck, and keep whittlin'!!!
-"Just like a buzzin' fly, I come into your life, I'll float away, like honey in the sun..."--Tim Buckley