I've tried to find a post in this thread but couldn't... I'm sure there's something somewhere (specific, I know) that says it doesn't matter about your long-haul inbound connection (you could take any BKK-DOH flight), rather it is all to do with when the next connecting flight is from when you land.

This would mean any BKK-DOH would work for STPC. However, I can't find the post confirms this!!!