@Matthew *****
No, when/if you switch to the income method for your second extension of stay when you’re able to show proof of twelve conservative transfer, this is the only way you show proof of sufficient income to support yourself in Thailand and you don’t need any funds in your bank.
However between the first and your second extension you’ll need to keep 800K thb in your account for three months after the extension is granted, it can’t drop below 400K and you’ll need to top up the 800K two months before you apply for your second extension of stay based on monthly income. This is just part of the deal when you used funds for your first extension of stay.