Someone suggested 'Mount Emei' for this connection, but which reclining buddha statue is meant (at which temple)?

Well, I don't think Mount Emei temple has any giant reclining buddha. And also I do not agree with Ayutthaya too. The famous reclining buddha of Ayutthaya is located in Wat Yai Chai Mongkon Temple which is not part of Ayutthaya World Heritage Area. The World Heritage Site of Ayutthaya covers only Ayutthaya Historical Park which is a western part of Ayutthaya Island, while Wat Yai is located on the east bank of the river and quite far from the historical park area.

For Giant Reclining Buddha in Thailand and part of World Heritage Site, I recommended Kamphangphet which is part of Sukhothai and associated cities.there is a large ruined of big reclining buddha made from leterite.

Thanks, Durian. I've changed it.