here is some elite doing a 6 stroke 25 m.
He uses a big scull in his pull to get extra traction.
Hand basically does not move back while body glides forward during his scull.
At higher strokerates there is no time for these tricks and wiggling the arm around much.
When doing doggy paddle the urge to scull becomes greatest i think. You almost start to wiggle your hand automatically under the body then.
scull start point