optimal job part refers to what the job of at least one of the members in you party has to be to receive a boosted/the optimal boost from this spell.
Own input: I have heard that this is acctually more like a spike effect than actual reflection but I have no way of finding out if this is true or not.
It has blaze spikes animation, but it's non-elemental damage, and with a PLD in the pt it was giving back anywhere from 0/1-35 dmg from what I noticed.