"Muzzle downrange means generally downrange, and does not have to be directly horizontal, pointing at the backstop, unless the WSB specifies it as such."
To me, 'directly horizontal' would mean barrel horizontal and parallel with ground.
So, 'generally downrange' would mean the barrel does NOT have to be parallel with ground. In other words, pointing at the backstop would be ok, as would pointing at the ground X yards out in front of the start position.
If a stage briefing says facing downrange, a pistol shooter must be square to the backstop, not leaning or twisting one way. For a PCC shooter, being left or right handed may be an advantage of having the barrel quicker to come up to the first target of a particular stage.
These rules give a match director the ability to start PCC division differently than other divisions.
Examples would be: obviously 'facing up-range with both wrists above respective sholders' vs 'facing downrange, stock on belt, muzzle downrange'
'hands on marks' vs 'muzzle on mark'
'pistol in box on table' vs 'PCC on table'
The only other instance I know of for start positions being different depending on what division you shoot came up recently at Pelham match, the briefing said magazine loaded but chamber empty. Not much of a question for semi-auto pistol, but how do you do that in a revolver? Revolver shooters were started with all the chambers loaded.
Remember, in USPSA, you compete only against others in your division.