Litter Tray Advice - 💩

This is my beautiful 8 month old cat. He’s awesome, and our first ever cat.

Recently he’s decided he only wants to poop behind his litter tray, and not inside it. He will literally move the tray until he can get behind it.

He will always empty his bladder in the litter tray without issues.

He is an indoor cat

He has a full clean bill of health from the vet and all his working/vaccines are up to date.

It’s always clean, and we use a really good quality absorbent litter which has been consistent since he was a kitten.

We’ve tried a different tray size but the same issue.

I’d love some advice - we were wondering if he might prefer a covered litter box?

Any and all suggestions or experience would be so welcome.