Forecast Consumption in previous month

We are using Advanced Supply Chain Planning (ASCP) and our forecasts are in monthly buckets. 

We want to include the previous month's forecast and Sales Orders.  We have no problem getting the Sales Orders to be included. 

BUT the previous month's forecast is ignored and so the previous month's sales orders consume the current month's forecast. 

How can we bring in both numbers for the previous month and 'force' the previous month's sales to consume the previous month's forecast before spilling into current month?

=====

We  DO  want to bring in the previous month's forecast. 

We DO spread the forecast evenly.  and we ALREADY use +30 / -30 to consume the forecast.