Hi,
Would it be possible for you to share the details about the full model fit to your time series, such as the PROC HPFARIMASPEC code and/or the Parameter Estimates table displayed in Forecast Studio? That information would be helpful in addressing your question. If you are not able to share those details here, then you might consider going through SAS Tech Support for further assistance:
http://support.sas.com/techsup/contact/
Thanks,
DW