5 tiles, but every visible non-friendly creature gets proced once, meaning surrounded moose will get mad instantly.
I’m not sure if I understand your idea correctly, but:
A pseudo-fear effect that would cause the moose to act as if scared if the closest non-friendly creature is within x tiles, but only if the moose is not mad.
That could work, but it would make them quite timid, only ever attacking if pre-triggered by zombies or if surprised. It would not change the way a set off moose acts, though.
Alternative interpretation:
A PLAYER_CLOSE placate effect with larger radius. Basically,
This one would have a negative effect of making “stared down” moose more timid than ones that got surprised, but it would give a sprinting player a chance to calm down the moose and make it stop charging.