ORIGINAL: John Redman
We like to have you keep it out of the 6 oclock position for the following reason. If you happen have any raw fuel in the combustion chamber at light off you will get a truely flamey hot start. All the fuel will be sitting on the plug and once ignition occurs you have a real mess. Other than that it won't have any effect on hte operation, it is just one of those "what if" safety items.
Reg. your theory about raw fuel and inverted mounted engine: Would not the raw fuel still be ignited a second later when the propane is ignited...?
I actually think it might even be safer to have it mounted inverted. One time I flooded my inverted mounted SimJet 3000, and it would not ignite because the glow plug was submerged in fuel... All I had to do was to hold the plane vertical and ran the starter a few times to drain the engine. Then it ignited safely on the first try.