Do we know these tables were based on experiment rather than conjecture/extrapolation? If tests how was the data obtained?
I don't know. Scharnhorst data show the distance from the gun to the point where the bomb fell and the distance to the point where the bomb stopped.
The data table is in the chapter titled Leichte Feldhaubitzen, 7 bis 10 Pfündige, but in the table there is a column titled Schwere des Mortiers.
Is it possible that he meant mortars here, not howitzers? Did the French use 6-inch and 8-inch mortars in the 18th century?