as I stated IF you are going to interact with Immigration during your stay you will be required to complete a TM30 and do your 90 reports or face being fined. You can ignore both and just bounce in and out every 180 days without any consequences IF you have no interaction with Immigration during your stay. Departing the country Immigration have no interest in TM30s 90 reports or your tax filing status….
Flown both Lufthansa and Austrian via Frankfurt,Stuttgart and,Munich direct and indirect into BKK. Never been asked if I have either a visa or a return ticket. But that doesn’t mean you won’t….