You would need to make up for 2,400 potency, and that assumes that LB2 hits all the targets. AF3 is, what, a 1.8 multiplier? 260 for Flare times 1.8. . . 468 potency, if I have the multiplier right? So, somewhere between the 5th and 6th casts it should make up, assuming that all potency is the same (which it isn't).