24 blocks is 24 blocks, doesn't matter what direction. I'm no expert in spawn distances but I'd say the green area is definitely going to be inside the spawn radius. Mobs will spawn 24 blocks above you, and I'm also pretty sure this measurement is diagonal as well. Basically, 24 blocks up on the Y axis then 24 blocks in either the positive or negative direction on either the X or Z axis will equal 24 block diagonally from whatever block you started on. I know this seems kind of long winded, and again I'm not even 100% sure how the Playstation 3 version calculates these things, but I hope this helps.