Did You correctly define the metal case around filter ? It is very important for this filter type. I don't know what analysis method use PARFIL to simulate the filter, but if it is a sort of circuit analysis (not EM-simulation), as I suppose - You can give not accurate results with PARFIL, due to this simulation method can't correctly allows the coupled lines effects. You can correctly simulate this filters only using the EM-simulation algorithms.
Best regards,
Kit-the-great