My son raced the full USPKS series on a stock KA also. He was competitive all year and set his fastest relative time in the final race. His lap times in the final race were 3rd fastest of the group. Even faster than his teacher – TJ :)
I don’t think you can leave any room for grey area in the rules. If your bumper is dislodged – a penalty must be enforced. I understand there will be circumstances where the drop down bumper gets it wrong, but I would rather deal with that than some of the dangerous driving.
Also, in the case of brake checking – that would be something the officials can watch for and enforce a time penalty for that.