How make human following player behind he

I can only make human following player, but how to follow behind player

PHP:

public function onMove1(PlayerMoveEvent $e)
{
    $player = $e->getPlayer();

    $pk = new MovePlayerPacket();
    $pk->eid = 3956;
   $pk->yaw = $player->yaw;
    $pk->x = $player->x;
    $pk->y = $player->y + 4;
    $pk->z = $player->z;
    $pk->pitch = $player->pitch;
    $player->dataPacket($pk);
    {
    }
}