By default, Minecraft mobs can look 16 blocks ahead to find a player. However, zombies can see 40.
With the following setting, you can change how 'smart' the mobs are. This is most useful in the Minecraft versions below 1.14 as they require the player to be in this range. In Minecraft 1.14 and up, this won't matter as much.
Code (YAML):
navigation-range
: 16
The enemy-health-percentage condition has been improved and will not even attack the player when he is too low!