It's got nothing to do with the thigh. Its the top of the knee, the kneecap, and the crease a the hip. Like dis:
It also has nothing to do with "parallel" or how big the guy is or how small, male or female. That's why they are required to wear a lifting suit. Not to pander to the gay community, it's so you can see the hip crease and also if your butt is on the bench during the bench press.
Top of the knee is easy to see with a wrap or sleeve being irrelevant. Its the bendy bit. You know, the knee.
To show you what I mean, here is the pic again with the top of the knee (A) and the crease at the hip (B).
Now, I don't want to get all pissy about this. It was white lighted and thats the standard that fed accepts, despite the rules of that fed. I'm just saying that a trained ref should be able to see depth, or lack of it, without resorting to video.
If the powerlifting community can't keep their house in order, it aint gonna get no respect.