@Chan *****
For your first one year extension the 800K baht has to be in your bank account two months prior to the application and three months AFTER the extension of stay is issued AND it can never drop below 400K baht at any point.
If you want to apply for a new extension of stay you have to bring it back in 800K baht again two months before your next extension.
If you want to switch to the income method for your second extension of stay, you’ll first need to prove twelve months consecutive transfers of min 65K baht over sea, and the 800K baht is again free to use.