Liar!
Liar!
I used to perform the ass-to-the-grass squats because I was fixated on achieving proper depth. But ass-to-the-grass is unnecessary. Below parallel is what you should be aiming for. The best cue is back tightness. If you lose tightness in your lower back when you're in the hole, then chances are excellent that you're too deep. If you're back is loose coming out of the bottom, you're in a world of trouble form-wise. Next thing you know you'll be performing good mornings and your back angle will deteriorate dramatically.
Rip doesn't appear to be overly concerned with depth other than getting yourself below parallel. I don't know what else to tell you. Adjust your back angle early in the rep and try to maintain tightness as much as possible on the way down.