Two separate instances today with WHM co-healers.
1. Level 50 Alliance Raid. See that they're using Cure and Cure II a lot to heal tiny bits missing. Notice them Cure I'ing me. Tell them that it's ok not to Cure I me, I'm fine. They do not listen.
2. Level 60 Trial. See that they're using Cure III to heal the tank, who is standing far away. Tell them that Cure III is an AOE heal. They do not listen. (I also think maybe they weren't using Lilies or Tetra but I can't be sure, I have no monkeys to sort through my damage log currently.)
I don't expect a reply when we're in combat but I'd hope you would stop, using Cure III at least, after noticing that the tank gains 0 health,,, Or maybe they assumed my lilies and tetra was them...
Had a very good SGE co-healer in my daily Ivalice raid so I'm not entirely unlucky.