@Jim *****
When you get your 1 year extension you sign a document that says you agree to follow the guidelines. The guidelines for a 1 year extension based on having 800,000 is that you will keep the 800,000 in the bank for 3 months after you receive the extension and never let it drop below 400,000 the rest of the year. Those are the requirements for the year after you get the extension. Next year the immigration will ask for 12 months of bank statements and they will check to see if you followed the rules. If you did not follow the rules, you do not get a new year extension.
Regardless of what your experience was, those are the rules. Many people who use the 800,000 method are denied their extension for the next year for failing to meet these rules.
You will also be denied getting your next year extension if you want to use the monthly transfer method because you broke the rules for your last extension.