This may have been the first time I’ve ever attempted this feat of strength. That being said, the behind the back deck of cards tear went quite well.
By changing the position of the hands, there is a bit less leverage than out in front. It’s a tougher angle from which to exert the force.
But in some ways, this was a little bit easier because my left forearm was posted up against my back. Posting is typically frowned upon in a deck of cards tear as it is cleaner to keep the arms away from the body. I’ll have to try it without the post the next time I give this feat a go.
For more on card tearing, including the basics see this article.
And for the deep dive, check out Jedd Johnson’s Card Tearing ebook.