Cash flow forecast issues regarding Purchase Orders on SAP Business One

My company imports products and we must consider more than one date to control delivery time. The system delivery time we use to control the date the goods will be available in my company and we needed to create another date to controle the date the goods must be shipped by the supplier, that will be obviously earlier than the date I will receive the good and have it available. This difference of dates is about one or two days for local suppliers and can reach up to 90 days for some imported products.

This situation causes a problem on cash flow forecast, because it consider it will be invoice on the system delivery date while it will be invoiced according the ship date.

I have tried to solve using A/P Down Payment Invoices on the invoice date (ship date), however it duplicates the payment on the forecast once it does not subtract the A/P Down Payment amount of the Purchase order payment on the cash flow forecast.

Does anyone found a solution for this problem?