How does one overheal exactly..?

[DreamWeaver]

not quite. iirc, single target healing gives 0.6 enmity per 1 hp healed, and double for every overhealed hp.

(also #1 method to reset mobs back when hunts were introduced)

False.

Per HP healed is always 0.5 enmity, regardless of overheal or actual heal.