I like pretty small tips with fillet brazing. Like really small. Are you using a Harris torch handle? Every company uses a different number system to indicate orifice size so I don't know how big yours is for comparison to what I like. However the flames on standard small acetylene tips tend to blow out from gas pressure blowback when getting close to the work when fillet brazing. Bigger tips less likely. The solution is Meco or Paige multiport tips that have a sharp flame and don't blow out nearly as easily.