see that thing i did there with putting the link in??
what can you see in the mirror to help your form? can you see your lumbar arch? no. are you checking out your knee cave? in that case you are looking down and doing it wrong.
i could tell dude in the vid was checking out the mirror even though the mirror was cut out of the vid.
(not meaning to pick on you OP the significant majority of dudes in the gym squat in front of the mirror).
people get that glazed over look in their eyes. disembodied. they can't feel the movement at all because their attention is riveted on (irrelevant things like how swole they think they look. trust me. it is a bajillion times hotter to squat in such a way that shows you can feel the movement. hard to describe... i think you need to feel the mind-muscle connection. or something. it is a bit soulless otherwise...