I can't say where the failure started on the failed PW3 cams I have. They were too far gone to tell. I have however seen the beginning of failure on several standard and combat cams where tired valve springs were likely the reason for failure that started on the closing ramp just after peak lift. Here is a trace of a cam that was used with exhaust valve springs that had deteriorated to ~50 lbs of seat pressure. You can see the point of maximum wear is just after peak opening of the exhaust valve. The purple line is the worn cam. The blue line is a new cam.