Overworld zombie pigmen spawns

With the new 1.3.1 version, do zombie pigmen spawn immediately adjacent to the nether portal in the overworld, or do they spawn anywhere nearby like mobs from a mob spawner?

ETA: I'm interested in clarifying the vague wording in the wiki, which states they spawn "near" a portal. Contrast the wiki entry for zombie pigmen:

1.3 Zombie Pigmen can spawn in the Overworld near Nether portals.

with the one for monster spawners:

While the block is active, it will spawn mobs within an 8 × 3 × 8 block area (8 wide and 3 high and 8 deep), centered on the corner of the spawner block with the lower x and z coordinates. Mobs can spawn anywhere in this range that is suitable, even if the immediate vicinity of the spawner block itself is not suitable. The horizontal distribution is nonlinear, with positions near the spawner more likely than ones farther away.

Solution 1:

Looking at the source code, near a portal means on the base of the obsidian portal frame. The pig zombies will also look in a completely random direction.