^That's quite plausible, and I appreciate the effort you put into the graphics. Why didn't I think of that? And maybe in the long shots, the person with the extinguisher was wearing some kind of safety gear, just in case.
Still, the problem with the "petered out" idea is that, as I said, the stream from the flamethrower is travelling pretty straight across that entire 25-30 feet, not dipping much due to gravity. So it must've been shot out at considerable speed and could probably have reached the rest of the way, or nearly so. That could still be consistent with your model #2, though. We only saw a couple of shots of the flame and vapor interacting, so they could've simply cut away before the flamethrower stream moved much past the front of the vapor cloud.