BTDT. I shot Nationals six or seven times. The cover rule was interpreted and applied differently each year, on each stage, and by each SO. It's why half of the stage walkthrough became shooters taking position and asking SOs "is this ok?"
FWIW, the original set of KSTG cover rules were:
- 50%; the competitor protecting at least 50% of his torso from any Threat target that has not yet been neutralized if cover is available (as measured from the center of the target)
- crowding; muzzle must not protrude past the uprange edge of the point of cover being used
- pieing; shooters must engage targets in the order they become visible around a corner (applies to vertical cover only)
- feet; both of shooter's feet must be in contact with the ground while shooting around cover (no silly IPSC 1-legged acrobatics)
The rules specifically prohibited warnings.
At our "beta match" we had multiple USPSA/IDPA national champions and the #1 complaint was the cover rule. Because of the lack of warnings, shooters frequently stepped into a position that earned them a 5s penalty for every target in an array. After the fact there's really no way to adjudicate... if the RO says you were an inch farther around the corner than you say you were, that's that. And it led to some pretty heated discussions.
That's why we switched from the subjective judgment of the RO to an objective fault line. But as mentioned in the first post, that has proven to have its own weaknesses.