I use my Engineer to farm mobs in Orr (usually the events around Penitant Camp and southward). When I attack with the flamethrower, I'm attacking usually a group of five or more Risen. I have not had any trouble 'tagging' each one as I run by spraying. Since AreanNet increased the flamethrower cone spray from 30% to 60%, I'm definitely doing great hitting targets. My playstyle, however, may not be like anyone else's. I normally do not stand still and spray - I run. I run in circles, run through groups (and flip around to continue spraying), and even run side to side spraying. Since the Engineer only wears leather armor, I find it best not to to try to "tank" mobs, but to perform hit and run and hit and run and hit and run maneuvers. My best defense, when an enemy launches an attack at me, is 'don't be there.' So many times, enemies are targeting where I WAS standing, rather than where I AM standing.
Does that playstyle increase the likelihood of hitting targets? Possibly. But ArenaNet's buffs to the flamethrower are probably helping, too.