The lean must be maintained throughout the arc to the plant/takeoff, as it allows the jumper to be vertical rather than leaning in toward the bar at the takeoff.
The drill simply involves running in a circle - with the left-footed jumper running counter-clockwise and the right-footed jumper running clockwise, while leaning to the inside of the circle.
Over the years, manufacturers have recommended various leaning strategies.
There's actually a placard on the panel giving leaning recommendations and restrictions.
He argues that the leaning method is easy to grasp and the engine is well cooled enough to tolerate some imprecision.
Whatever the case, the TAT leaning strategy couldn't be any more in the face of Lycoming's recommendations.