Whether the vehicle tie downs are crossed or uncrossed doesn’t matter when it comes to load shifting.. If one side breaks, the other side can become slack. It’s just which way that changes. I like crossed since there’s less loading per unit length of strap/chain than with uncrossed. A longer strap experiences less strain per inch than a shorter one. Crossed straps are inherently longer and therefore experience less load per length. That said, they can stretch more too...which is why if they are straps rather than chains, they need to be checked for correct tension frequently while traveling to make sure they haven’t stretched and become loose.