How far can Minecraft mob pathfind

I'm building a custom mob farm in MCPE v 1.1.2 where the mobs try to walk over open trap doors but fall in a water stream. I'm wondering how far mobs can pathfind so that if a mob is at the edge of the farm it can pathfind to the other edge.

Solution 1:

According to this site under the "Behavior" tab, zombies can chase the player from up to 40 blocks away, however, all other hostile mobs will only detect the player from 16 blocks away (except for endermen and zombie pigmen. They have to be provoked). So, if your trap is small enough, you can stand at the end of it and letthem come to you.