I tell all of my clients, if you have any doubt what the filing fees are, ask the Recorder's Office.  I have found, here in Kansas, that they are very willing to tell you what they are going to charge.  Here, the mortgage tax is charged on the amount printed (maximum amount) on the front of the mortgage.  If the amount is specifically set out as interest and principal, they charge on the principal maximum amount.  I hope this helps.