I think it has more to do with fuel air ratio...When you change the orifice you are effectively "adjusting the carburetor".
Huh, I wouldn't have thought ratio would be a consideration since the combustion isn't enclosed like an engine. There's just gas and endless air around it making their own ratio at the flame. Is there a venturi in there? Don't see why you couldn't just sight the flame and make adjustments to a regulator on the bottle. I'm imagining things like stoves, water heaters, etc.
The smaller jets thing I got from continuous hot water heaters I got for cheap. Bosch or Rinnai, can't remember. Still haven't got around to them. They are dual gas units, though, so could have been purpose built. Other than metering in the fuel gas to the burner, differences I can think of would be piping for propane pressure and burn temp tolerance.
