I am not sure of using the word "correct" nor do I think I would be very concerned about a fork truck if I had any chance of a propane fueled fire.
I think I might use the phrase "best practice" to refill a tank -off- the vehicle so as to be that much more sure of not having a hot exhaust or any other possible spark any where in the vicinity of the refueling operation, but I would spend far more effort in getting the operator or whomever is changing the tank, in getting them to run the fuel out of the hoses on the truck after shutting off the tank's valve, so as to not having any fuel escape, than in worrying about where the truck is properly parked.
Which do you consider a greater fire hazard, the fuel escaping when the hose is disconnected to remove the tank, or the fuel escaping when you bleed the pressure and remove from the fill hose?
my answer is that if the fuel might be ignited, it burns at the same temp, and doesn't matter to the fuel or the spark which hose it came from last.
While I appreciate your effort, Joseph, I seriously will be very surprised if you are able to find anything [I have not] in the NFPA regs.
You may also be able to check the NFPA regs by checking with your local municipal fire department's "inspectors" or "fire marshals" office.