How recently did you adopt him? Bunnies are a lot like teenage kids and go through a rebellious streak. There could be quite a few reasons for his spraying.
Bunnies mark territories. New territories get a lot of attention, especially if there have been or are other animals in the area. It’s just what they do. Sophie is perfectly littertrained but if I take her to a friend’s house that has a bunny, all litertraining goes out the window and she’s peeing, pooping and chinning EVERYTHING in site as if to say “I was here!”.
You can’t put the litterbox where you want, as you have now found out. Your bunny wants the other corner for its bathroom. That should do the trick with that problem, and honestly, i think the spraying is just the initial marking. I recommend only having one room or two that your bunny goes into. If you let it into another area of the house, or move his cage, you will find that this will happen all over gain. Good luck!