Currently in X3 there is the ability on the Product level (Sales tab) to be able to specify an item as a back to back or a Normal through the Back-to-back order field (ITMSALES.CTMFLG_0) field. A nice enhancement to the system would be if the user had the option of setting this parameter on the Product site level. We have some clients for which their order fulfillment method varies on a site by site basis.