I actually prefer them under the duvet as it is easier to roll over. When they are on top I feel like I am strapped into bed with their weight. I do, however, draw the line at the dog getting under the duvet - he stays on top, but since he rolls into a tight, self-conscious ball when he is allowed on the bed, on a queensize he represents no real difficulty, despite being a large dog. On the caravan bed, he takes up way too much room so is only allowed on when the heating fails ...