This is a worthwhile report for this situation: Inventory - Sales Back Orders
In general the “Qty. Outstanding” is the main driver. Given that you can use reservations this adds another layer into the mix as a reservation can be on stock but also types of supply - PO’s, production orders, assemblies, transfers. If reservations are in use you would want something to assess that level of the data too. Would in essence give you a breakdown of things on back order that are planned and not planned from a supply stand point.
