In a previous post we had a look at the effect of the backward demand time fence. There is a parameter that you might want to investigation in conjunction with this called the ATP delayed demand offset time. If you are considering the delayed orders then you might want to evaluate if you considering them being shipped out today when ATP runs or some time in the future. In effect you are favoring new orders and allowing delayed orders to wait a little longer so you will have to consider how this works for your organization.
Keep in mind that in this walk through we set the fence at the accounts receivable parameter but you can specialize on an item level at the default order or site specific settings.