To change from extensions using money in bank to using monthly transfers is a pain for those with embassies that do not provide "income letter" eg UK, USA, AU being 3.
You need to run both methods in concert.
I'm my situation I'm currently doing the monthly transfers PLUS also satisfying the money in bank option.
Next extension (Nov) I will show compliance with funds in bank and 12+ monthly transfers from abroad.
Then following year just do the monthly transfers.
From then on as mentioned my "immigration bank account" will have small balance.
On 14 of every month I do the transfer using WISE app from my Oz bank account app.
The transfer is instant and lands in my Kasikorn bank account.
I say to my Thai partner ..."money come"
She goes to ATM (Kasikorn in our condo building) and transfers the funds into her account.
Any non immigration matters eg purchase of car/real estate/medical etc is done in same way.
BTW: not married..