In my imaginings I used to be extremely strict about the whipping post: it had to be a stone pillar, tall enough that the victim's arms could be nearly taut above her head, and wide enough that there'd be an element of hugging the post. I liked that moment when one arm was released and, exhausted, she would fall, too weak to stand, hanging by one wrist. I've become a lot more liberal now - probably since Passion of the Christ - and have come to appreciate variety: the shorter post so the victim hunches, or some kind of rail so the victim's arms are pulled out to the side, so even the wrists fastened just above the head so when exhaustion comes she falls, knees bent and the arms stretched.
The nature of the lash, of course, is important. In my strict days it had to be the proper flagellum, with lead and bones tips, but I've liberalised to allow a knotted multi-tail whip, a bullwhip or a cane. And when to perform the lashing? The night before execution? The morning of execution? After the march to the site of execution? And where? In the jail? In public? Do you want the victim still almost pristine as she begins the parade, beautiful and strong enough to carry her cross, or do you want her already weakened and in agony? In The Scapegoat I compromised by having her carry the beam naked to the marketplace, scourged there, and then dragged outside the city for crucifixion. There's also the question of when the worst of the mockery happens - fit the crown of thorns while she's still fit and healthy and will feel most shame, or when she's been whipped and may not be fully aware of the humiliation?