Keep your head down is very restrictive, that advice inhibits the free flowing of the arms and hands into the follow thru creating a middle of the swing. You look like an archeologist studying what’s down there. Allow the eyes to follow the ball, keeping the arms freely accelerating past you on the way to the finish. Keeping you chin off your chest is best, chin up clears the chest and shoulders to move thru the ball more easily.
Animals in the jungle keeping there head down get eaten!