I would start depositing the 65k around 2 months prior to you renewing your extension with the 800k , and then after you have your 12 × 65 k , go in with the appropriate paperwork. ...
My Thai stepson has both Thai and Oz passports , on his last trip into Thailand he entered on his Oz passport ...had to go to immigration when he looked at his entry stamp and realized he had 30 days ... costly unnecessary mistake
then here's a thought ...might help , get your pension paid into your account in your own countries bank on that 30th / 31st , then you do a transfer in the first day or so of the new month into your Thai bank ...it's the only way around your problem of a government pension paid then