Reprisal (-10% damage on enemy) on raid wide abilities already casted but not blown

[Boys]

Like in current moogle roaster - Containment Bay P1T6. That raidwide "distance" aoe ("proximity" actually) which is placed on ground almost at the start. Does its damage get reduced if I use reprisal on boss AFTER the aoe was placed? Pretty sure there's other similar conundrums in the game beside the aoe type. Lazy to test myself, thanks.

[aodhan_ofinnegain]

General rule of thumb is you need to apply, Addle, Dismantle, Feint and Reprisal during the cast or before the action if no cast bar, for the mitigation to apply.