In a proper squat your knees are most exposed about halfway down. So that’s where you tell your patients to stop their momentum and contract everything so that they can get the bar going the opposite direction? If you want your patients to do squats without knee pain your efforts would probably be better focused teaching them to bend correctly so that they’re not using the knees that much in the first place but rather are doing it 80% with the posterior chain like you’re supposed to.