of course opinions can differ, but the rules are what is relevant even if not always enforced. When they are, it's no good saying but Joe Blogs said he's never been asked.
just checked my flight number, from UK is not same as my arrival flight number! So would probably be the country I transit through as the flight originated there. Not at all sure. Lol. I think I'll stick with Heathrow as that's where I start my flights.