I have also experimented with that, and apparently the whole AddMovementInput() func altogether does not really care about the magnitude of it’s Scale argument, it only cares about positive/negative values, setting the direction. It is really a flaw, because it’s argument list and documentation clearly state that the function can and should set the movement speed, not just direction.
Let’s wait for an official answer. I would also like to hear a workaround for this.