Minecraft wiki entry for Spawn, associated text: Charge raising mobs add the charge in a sphere around them. This occurs farther the charge cancels spawns. Mobs' charge spheres don't cover each others' up, but stack, affecting areas further away, given the mobs are in proximity. The charge set by 1 mob is the same throughout the block the mobs resides in and the block south, east, and southeast adjacent to it. From that, charge prevents spawns within 6 blocks straight between them or 4 blocks along a diagonal, given no other charge affecting mobs are present.