Calculation fields ignore the portal filter and evaluate solely by what you have defined in the relationship for that portal.
A summary field defined in the portal's table can produce totals that will be consistent with the portal filter.
Can you explain a little more detail on your commnets:
"A summary field defined in the portal's table can produce totals that will be consistent with the portal filter."
My summary is on the portal's table whcih is
SumQty defined as =Total of ThisShipQty
BUt, it sum all records, which is linked from parent record, and including filtered records.
I don't know your relationships in use so posting that info would help me explain using your actual relationships.
If you have this relationship:
Then putting PortaltableOccurrence::SummaryField in the portal will display a value that correctly reflects any filtering that takes place due to a portal filter.
Defining a calculation field in LayoutTable that refers to fields in POrtalTable, will ignore any portal filtering.