Hi Halaban,
during acceleration palm should be under Lever,and correspondingly during deceleration over Lever.
I have only seen that procedure written in one company's OPS Manual.
I find it strange that with Thrust Levers, Speed Brakes, Control Column (side stick) all needed to be moved forward to accelerate, why anybody would pull the flaps lever in the opposite direction whilst accelerating.
I think that if someone gets confused as to which way to move the flaps lever in the first place, then they would rotate their wrist to the recommended position and still move the flaps lever incorrectly.
The big advantage of the procedure is that it gives the PF a chance to observe the intended movement.