Flamethrowers aren't that good in this MU , even if you AA them they only eat 8% wich will not scare them to Jip again , use AA 1 and punish with a full combo , force them to play footsies , this is the area where you got advantage.
B34 , F2 and B1 are your best friends here , learn the optimal range for b(3)4 to not whiff ( here's a tip , do u34 on a standing sub zero , that leaves you in the perfect range for b34 or d3 ) , if Sub likes to put many ice clones just wait for him then zone him and start looking for 3 things: slide , jump in or freeze and react accordingly.
Use d3 when you think he's gonna d4 / 22 / 21 after blockstrings , since it's 7 frames you outspeed all of his moves , also if you interrupt his d4 with a d3 you get a free b3 / b34 or you can go back into the spacing.
Always maintain yourself a tip outside of jump distance where you can react to either a jumpin or a freeze while spacing him with f2 / b1 and b3 , he can't do much other than:
1 risk a jump ( AA )
2 throw out a random freeze for a trade ( again don't use flamethrower at this distance because it can whiff and you eat an iceball ) wich you can duck by d3 / d4 while dashing forward to hit him or jump back iatu.
3 guessing an Ice Clone wich puts him back to almost fullscreen asking to be zoned / baited
4 dash in d4 / 22 / 21 wich you can space and whiff punish with either b1 / f2 / b34 , just keep walking back and forward to make him second guess him
5 Random slide wich you can block and punish with b2 Tu
Also d4 into freeze will go over you d3 poke since it's an high projectile , and if you block a freeze from sweep distance you can punish it with a full combo with b2 / dash 12b1 / b34 , i also think you can punish ( or at least force him to block ) a jump distance freeze with f2.
Keep working on that Sektor STH and you'll realize this is a clear 6-4 in Sektors favour