Unfortunately the rules are not the rule. Rules are consistent. Decisions from immigration offices are inconsistent.
Even this knowledgeable web-site is not always expert as they speak from THEIR experience and knowledge which can never cover every immigration office in Thailand.
Robert Lagas, for the previous 10 years on Non-O AGE extensions Mae Sot, and now Sukhothai, immigration have required 800k baht in my account for 3 MONTHS prior to extension.
I have questioned this on occasions with the same answer. Even as recently as May this year I was given a print-out of the new rules and that STATED 3 months prior.