My 2 cents.
The question is have you maintained an annual earnings and deposit totalling 800K.
Any funds in the bank used for the combination must have been deposited for 2 months prior to the date of application, the same as if using just the fund's method.
To quote yourself, if your income was 500,000 throughout the year, then the fund's requirement would be 300,000 for 2 months prior to the date of application.
If your funds, we're only 280,000 throughout the year, and you top up to 300,000 2 weeks before your extension, then in my opinion you don't qualify.
However, it is not for members to make a decision, we can only quote the rules, the decision is at the IO's discretion.
For what it's worth, my IO insist the funds must be 400,000 when using the combination method. (Their interpretation).
Order 548/2562.
(4) At least 2 months prior to the filing date and at least 3 months after being granted permission, an alien must have a deposit in a commercial bank located in Thailand of no less than 800,000 baht. After being granted permission for 3 months, an alien can withdraw the said deposit and must have the remaining balance in the bank account of no less than 400,000 baht or
(5) Must have an annual earning and a deposit in a commercial bank located in Thailand with totalling of no less than 800,000 baht as of the filing date. The said deposit must remain in the bank account prior to and after the permission is granted and the withdrawal can be made under the same condition in the Criterion (4)