Thanks for your reply Erin.R. That is what I thought. Quite some time ago I changed his setup so that everything is as flat as it can be for him. He was in two Zoozone 2s connected by tubes, but recently I dropped him down to one as I felt he was struggling (but still felt compelled to visit all of it, bless him). He seems reasonably content in the single zoozone2.
He is sleeping more as well, in the evening he'll pootle a bit, then snooze, then pootle a bit more. His weight has always been very consistent which is great, now he's older he gets a little yoghurt drop or a chocolate drop every day, which helps to keep his weight stable, needless to say this is the first thing to go from the food bowl