Hip-Drive Assistance/Knees/Proper Stretch Reflex @ Bottom of Squat

[agalig]

Lets see if I have this right:

During a squat with proper form-
Lumbar and thoracic spine in extension
Thighs parallel to feet
Weight distributed over middle of the foot
First part of the movement is sticking your ass out
Lower pelvis (acetebulum) below than top of the patella

Now the hardest part for me is the stretch reflex at the bottom of the movement. It feels like I'm using my knees way more than I should, instead of driving up with my glutes. In your experience, what is the most common cause of poor hip drive/use of knees on the ascent of the movement?

[Mark Rippetoe]

Your knees are too far forward at the bottom, the result of your misunderstanding of the first part of the movement. The hips go back at the same time as the knees go forward and out.