"But during the take off, I was told to keep my feet on the floor in order not to kick out the max autobrake during rejected take off."
How do you tackle an engine failure in such a case? You would definitely need a lot of rudder to counter the yaw, but with half your foot resting on the ground, that seems to be quite a cumbersome task. Or do you lift your feet off the ground and then rest them entirely on the pedals? That would seem to be wasting precious milliseconds.