Depends on the situation.
Situation #1 - Leveling/Grinding
If you have a tank/taunt, cast 1 overheat near him while he is on “block” stance (pressed C) and 1 near DPS. BUT! But if you see that the tank still have more than 80% of his HP, dont put it yet. Put it when there are 1 or more player who have 60% hp or less. If you put 1 Overheat, cast another so while you wait, cooldown is ongoing so you can have heal in another 20s.
Situation #2 - Siau Mission
Look at the position of the boss, put 2 overheat of heal tiles on 1 place only. Not too far and not too near the boss. If you are too kind and your party member sucks, remind them where the heal tiles are. Example, “Heal at right/north side”. When the boss runs/move, move the place of where you put the heal tiles. Party members will go there automatically when they have less than 90% hp coz non-healer char are too afraid to die when they received 1 damage. Yes! They hog the heal tiles while only receiving 2 digit damage. Always prioritize your heal on yourself. A dead healer is a dead party.
Situation #3 - World Boss/ Field Boss hunting.
If you are full support, put heal tiles near your DPS. If possible, put safety zone near/on him, put 2 overheat on his place, go away on safety zone/leave him alone on safety zone so block count will not deplete fast. Always turn on the “Remove Heal damage” attribute so only character can only receive your heals, not damage the monster.
Situation #4 - Dungeon runs
If rush, same as situation #2. If full, same as situation #1.
Situation #5 - ET
Depending on floor level, put heal tiles when they finish cooldown. If you have a chrono on your party, when he/she cast Pass, put another 2 overheat of heal. And, DON’T DIE! A dead healer is a dead party/failed ET.