Paul, If you set the "One Inventory Facility" flag to No, the system will try to reserve inventory from the first facility in ProductStoreFacility list that can totally reserve from. If there is no facility with enough quantity, inventory will be reserved from the first facility in the list ProductStoreFacility list.
So, If you have another algorithm for reserving inventory from multiple facilities, you have to modify reserveStoreInventory service. If there is no algorithm for reservations and the user needs to choose every time the facility during order creation, you can modify product view screen in Order Manager and let the user to choose a facility from a list of facilities for every product. Then pass this parameters to createOrder service, and then to reserveStoreInventory service to override the reservation facility. Just my 2 cents Bilgin
