Credits to @Wedge_Antilles for this find. If you do a cl.hk xx lp AE, you get a +6 on hit frame advantage on fei long.
I did some testing and here is what i found.
Close hk (2 hits) xx lp fireball gaining +6 advantage on hit:
Works on fei long, Cody, ibuki(corner) dudley(corner) Rufus (midscreen)
doesn’t link at all against akuma, gen, Sakura, oni, elena, feurte
Few combo possibilities in the corner are:
J.hk, cl.hk xx LP AE, Cr.hp xx Hp Rekkas
417 damage, 655 stun. Meterless
J.hk, cl.hk xx LP AE, Cr.hp xx hk Dp
420 Damage, 700 stun, Meterless
J.hk, Cl.Hk xx Lp AE, Cr.hp xx mp AE x FADC, Cl.Hk xx Hk Dp
489 Damage, 790 Stun, 2 bars
J.hk, cl.hk xx Lp AE, Cr.hp xx Mp AE x FADC, cl. Hp xx EX LMT
508 Damage, 750 Stun, 3 Bars
J.hk, Cl.Hk xx Lp AE, Cr.hp xx Mp AE x FADC, Cl.Hk xx EX Rekkas, Ultra 1
516 Damage, 760 Stun, 3 bars, full Ultra
J.hk, cl.hk xx lp AE, Cr.hp xx EX AE x FADC, cl.hk xx lp AE, Cr.hp xx Hp Rekkas
530 Damage, 840 Stun, 3 bars
J.hk, cl.hk xx lp AE, Cr.hp xx EX AE x FADC, cl.hk xx lp AE, Cr.hp xx Hp Dp
537 Damage, 860 Stun, 3 bars
J.hk, cl.hk xx lp AE, Cr.hp xx EX AE x FADC Ultra 1
580 Damage, 640 Stun, 3 bars, Full Ultra 1
J.hk, cl.hk xx lp AE, Cr.hp xx EX AE, Mk dp x FADC Ultra 1
580 Damage, 690 Stun, 3 bars, Full Ultra 1
J.hk, cl.hk xx lp AE, Cr.hp xx EX AE x FADC, cl.hk xx lp AE, Cr.hp xx EX Rekkas, Hk Dp
542 damage, 865 Stun, 4 bars
J.hk, cl.hk xx lp AE, Cr.hp xx EX AE x FADC, cl.hk xx lp AE, Cr.hp xx EX Dp
543 Damage, 866 Stun, 4 Bars
J.hk, cl.hk xx lp AE, Cr.hp xx EX AE x FADC, cl.hk xx lp AE, Cr.hp xx EX Rekkas, Hp Rekkas
545 Damage, 860 Stun, 4 bars
J.hk, cl.hk xx lp AE, Cr.hp xx EX AE x FADC, cl.hk xx lp AE, Cr.hp xx EX AE, Cr.lp xx lp Rekkas
549 Damage, 860 Stun, 4 bars
J.hk, cl.hk xx lp AE, Cr.hp xx lp/mp AE xx Super
561 Damage, 610 Stun, 4 Bars
J.hk, cl.hk xx LP AE, Cr.hp xx mp AE x FADC, Cl.hk xx mk dp x FADC ultra 1
561 Damage, 750 Stun, 4 Bars, Full Ultra 1
J.hk, cl.hk xx lp AE, Cr.hp xx EX AE x FADC, cl.hk xx lp AE, Cr.hp xx EX Rekkas, Ultra 1
575 Damage, 845 Stun, 4 bars, Full Ultra 1