Change mob attack range

Hi.

Is there a way to change the mob attack range? Right now, they attack if you are in a 16 radius. I want mobs to attack you in a, lets say, 20 radius when sprinting.

I've tried some things without succes. This is in the EntityMob class:

 protected Entity findPlayerToAttack()
    {
        EntityPlayer entityplayer = this.worldObj.getClosestVulnerablePlayerToEntity(this, 16.0D);
        return entityplayer != null && this.canEntityBeSeen(entityplayer) ? entityplayer : null;
    }

It should be done in this:

@ForgeSubscribe
public void playerSprinting(LivingUpdateEvent event){

	if (event.entityLiving.isSprinting()){

	}
}