There's always a math answer to when and where to heal. Its just a matter of having the right information.Nothing personal but damn how I hate it when people say "this is a HPS gain and this is a HPS loss". Healing is so much more about adepting to a situation than toping some healing meters. Healing the right targets instead of the ones that'll give you the most HPS is everything while healing. Say for example that a warrior and a fire mage is dropping low, the mage sits on about 20% HP and the warrior on 40%. Most healers would heal the mage first and the warrior after that and that's what differs a good healer from a bad one. The good healer would heal the warrior first and the mage after that as he/she is thinking of Cauturizing that will save the mage whenever happends.
So, healing the right target > healing the ones who gives most HPS.
That said, healing 2x flash and then a PoH might be lower HPS, but there is A LOT of situations where this is the very best thing to do. (spine HC with one debuff and a turn inc without SL anyone?).
HPS/HPM isn't about topping meters. (Neither is DPS). It is about making the right choice at the right time, which is what we are talking about. HPS/HPM calculations help us make the right spell choices at the right time. The highest HPM choice is almost always the right choice to make.
Right targets - this gets to the art of healing, and that is assumed in any mathematical discussion. Whenever you are talking healer math, you are always assuming that you've already chosen the right target. Now the question is "what is the right spell for this target?" And the math can answer that.
You say the choice is between the Mage at 20%, the Warrior at 40%. You chose to heal the Warrior, but didn't notice the Mage's cauterize wasn't up yet and lost the Mage because you were being cute with mechanics (even if cauterize procs, you'll need to heal that Mage again in 6 seconds or he'll die anyways). We aren't talking math, and it doesn't invalidate any math because the math only comes into play once you've chosen a target.
The math is for evaluating spell choice - I have three targets I need to heal quickly - do I Flash Heal them three times, or do I Flash Heal twice, then cast POH, or do I simply spam POH? Notice that in order to even ask a math question, the target choice is already assumed.
Nothing personal, but I hate it when healers get on their soapbox and reject any kind of analysis out of hand because healing is supposed to be something mysterious and touchy-feely.
There's an art to healing. But that doesn't mean there's no place for math.