Setting up Standard Rates in Advanced Benefits

What are the differences in the "Communicated Amount", "Defined Amount", "Estimated Per Pay Period Amount", and "Per Pay Period Amount" selections in the "Value Passed to Payroll" field on the Processing Information tab of the Standard Rates form in Advanced Benefits?

And on a side note, how are the "Communicated Amount" and "Defined Amount" fields derived on the "Amount" tab of the Non-Flex Program Enrollment form?