The above given link looks old. But the section: 4 given in it looks interesting.
The chunk traversal order is unique for every chunk the player is in, but there is one exception. If the chunk (0,0) (blocks 0,0 to 15,15) is one of the 81 chunks visited, it will always be the first evaluated. This can be exploited. Regardless of the terrain, there is a 100% chance the algorithm will not bail out before getting to this chunk. This means that chunk (0,0) has the highest chance of spawning mobs than any of the other 8 chunks. It's as high as CleanRoom.
To illustrate this, I built a 19x19x64 tower over chunk (0,0) with 16 spawning floors. After a couple of minutes there were about 150 mobs in the tower, and there probably would have been more if the cap hadn't been reached. (glass was hacked in with NBTForge for your viewing convenience. Original walls were rock.)
This technique should work on any map, and if I'm not mistaken, SMP, too (as of yet unverified).
I don't know if this exists for minecraft 1.9, this is fixed, or maybe it is not vanilla.
Is it true for minecraft 1.9?