I'm not sure if you understand just how bad the flamethrower's spread is, because it's literally about 1.5~2 times as much as the minigun's. A great example a few days ago: I went to puff'n'sting a medic on granary when he had his kritz charged, with the intent of picking him off before his patient could do anything about it. First puff, take out the axe, and to my surprise/misfortune he wasn't on fire. Bad particle, too far away, let's try that again. Take out the flamethrower, puff again at near-pointblank, whip out the axe, and...he didn't light that time either. At this point I'm positive his soldier's realized something's gone wrong, so I add more flames and airblast again...only one particle hits and the soldier kills me, then gets kritzed and wipes the rest of my team.
Stuff like that happened to me as well. I believe that this is a whole other problem: The damaging area of the fire particles does not coincide with the visual fire, where an enemy that is within the flame visual is not hit by a particle while merely being close to the pyro can mean you'll get lit on fire, especially if he is moving erratically. Actually, why am I saying this, you know this better than me. :derp:
To change
that, the mechanic would have to be revamped entirely, but that is not going to happen, is it?
What I meant was that aiming somewhere else than directly to where the target will be when the flames hit will make less particles hit, but if you
do manage to hit with more of them, you would deal much more damage. However, now that you have reminded me of the visual problem, I see that this is a bad idea.
Although, really, why is it that there are seperate particles for visuals and effect? Why doesn't valve make it so the damage particles have a distinct visual component, and that this way you can always see where your actual damage is going? You could keep a gentle permanent graphic effect coming from the flamethrower but have the main meat of the flame visuals come from the damaging particles themselves. And if that looks weird/bad with the current particle behaviour, then the particle behaviour would need a change.