It is not easy for most people of moderate income to send money back to the home country just to send it back as a top up. Not easy in the sense that (as was pointed out) it could be detected with just a bit of examination of funds transfer records to another bank or direct to overseas. Wealthy people could do this with ease but wealthy prople don't need to do it. It is more than obvious that the I/O just wanted to create a barrier that could not be gone around. I have read about other instances where a top up was allowed without question as long as it was proven to be an International Transfer. So again this shows a total lack of standards - no consistency of rule application from office to office.
- Unfortunately - individual airport and border I/Os and their Supervisors can make the rules strict or loose depending on their local interpretation. There does not appear to be a list of standardized rules - a check list to allow a traveler to be able to predict with some degree of accuracy what they will face. Standardization, consistency and predictibility are not known concepts in the world of Thai Immigration.
The Exemption Entry allowed by Land Border crossing is two per calendar year. But no official limit by air. In reality 3 to 4 by air could get you pulled aside and denied.
And as may have been pointed out - once the O-A is issued, the money that has been in the home country Bank can be immediately taken out. Because it will not be checked again by anyone. If you go back home in two years you put 800k baht equivalent back in an account for 3 months prior to applying. Or use the 65k equivalent) monthly of money that has hit your home bank account, even if it went on to Thailand. Or in some cases pension / retirement income records are allowed. Check with the Thai Consulate, you deal with.
With an O-A the one year clock starts with the issuance. Advised to time getting the O-A Visa close to date of departure - don't get the O-A Visa then wait two months to leave for Thailand - = time lost in the 1st year