Display Aging column in Open purchase order report

If I set preferences > Graphs and reports > Aging reports > Age from transaction date, then I understood how QB calculates the # of days from the PO date

However, if I set the preferences to Age from due date, I do not understand the calculation for the # of days

In attempting to work it out, I manipulated different dates in a PO, yet the # of days that was displayed did not match an aging from any of the dates on the PO

For example, I changed alternately the PO date field, the Expected date field (which I added to the PO form), and even in the Preferences > Bills > # of days bills are due after receipt

I understand that PO's are non-posting, which further confuses me as to how QB calculates the aging date if there are no recorded bills

One PO had been partially fulfilled, but the QB calculation did not match aging from the receipt date either.