having given this zero thought, and not familiar with the faster at lower premise .... since airr is what affords the bouancy (lift), and given that displacement (mass) of the aircraft is fized that the amount of air one needs to displace under versus over the wing would be greater the less dense the air to achieve the same amount of lift.
In short, couldn't more of the thrust be used to go forward versus up in heavier air ( that the trim of the wing flaps could be shallower) effectively reducing the drag caused by generating lift.
I should probably have read your aeronautics lesson first.