They definitely want to see 40K+ Baht every month, so he would need to have his pension deposited into his Aussie bank, then transfer (Wise, etc) the +40K amount monthly, with proof these were international transfers.
But, have Immigration stopped asking for proof of the "origin of the funds" in some/all offices for Marriage and/or Retirement incomes?
In the case of the OP, I assume his documentation of Aussie pension would work, even if the distribution frequency/amounts do not exactly match his Thai bank foreign-transfer deposit-record, provided the total exceeds 12 X 40K Baht.
