Every arrival from outside Thailand is a new arrival for all foreigners. The law upon which it is based doesn’t differentiate by the type of stay permission you have.
Doesn't it mean he is not yet under the new rules (effective 1st March 2019) and the dip below 400k won't apply to his current extension. He only needs to have the 800k in his Thai account 2 months prior to his next extension.
Yes, for land border bounce it's straightforward as Immigration knows you can extend by 30 days. For airlines, some do not care and want it within 30 days.
You shouldn’t have a problem with doing a land border bounce to get a 30 day visa exemption and then extend for another 30 days, but you should have proof of an onward journey within 60 days of entry. Flying adds a little bit more risk should you be denied.
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