I'm driving my disabled neighbor from Chumpon to Ranong because he wants to bounce out and in. Anyway He's a Belgium passport holder. He tells us he came in on a 30 day VISA on arrival stamp 3 weeks ago. I suspect he's confused it with a VISA exempt. If he in fact came in on a visa exempt can he get his first extentention at the Ranong immigation office even though he flew into Suvarnabhumi where he was stamped in. I'll try to get a screen shot of his stamp today.
TLDR : Answer Summary
A Belgian passport holder who entered Thailand with a visa-exempt stamp can apply for a 30-day extension at the local immigration office in Chumphon, where he is currently staying. The place of entry into Thailand does not affect his ability to extend his stay; what matters is his current location and registration.