Redis Cluster performance not increasing linearly with Lettuce

Question

Redis Cluster performance not increasing linearly:

Ran the perf on GCP Cloud: Machine Type: c3-highmem-4 (vCPU: 4 Memory: 29GB)

Standalone Redis: SET ops/sec: 243,858 (243K) {benchmarking using memtier_benchmark tool}

5 Node Cluster: Machine Type: c3-highmem-4 (vCPU: 4 Memory: 29GB)
All nodes are master, no replica. SET ops/sec: 1,011,661 (1.01M) {benchmarking using memtier_benchmark tool}

Running memtier_benchmark from Two 44 vCPU Machine: SET ops/sec: 567940*2 = 11,35,880 (1.13M)

On 5 Node cluster expected ops/sec according to linear scale: 243858(standalone Redis SET ops/sec) * 5 = 1,219,290 = 1.2M ops

Here expected ops: 1.2M, Achieved ops: 1.13M (Proves that Redis scales linearly with shards)

When ran perf with lettuce client, received the similar ops with standalone Redis with same latency. But with 5 node Redis cluster, got max 900K ops/sec with p99: 3ms and p99.9: fluctuating b.w 3ms to 100ms.

Code used to run SET command on 5 node cluster:

public static RedisClusterClient getRedisClusterClient(RedisClusterProperties properties) {
    List<String> nodes = new ArrayList<>(Arrays.asList(properties.getNodes().split(",")));
    List<RedisURI> redisURIList = nodes
            .stream()
            .map(node -> RedisURI.create(node, 6379))
            .collect(Collectors.toList());

    RedisClusterClient clusterClient = RedisClusterClient.create(redisURIList);

    ClusterTopologyRefreshOptions topologyRefreshOptions = ClusterTopologyRefreshOptions.builder()
            .enablePeriodicRefresh(1, TimeUnit.HOURS)
            .build();
    clusterClient.setOptions(ClusterClientOptions.builder()
            .maxRedirects(0)
            .topologyRefreshOptions(topologyRefreshOptions)
            .build());
    return clusterClient;
}

    private final StatefulRedisClusterConnection<String, String> connection;

    public Repository(RedisClusterProperties properties) {
        RedisClusterClient redisClusterClient = ConnectionFactory.getRedisClusterClient(properties);
        this.connection = redisClusterClient.connect();
        this.connection.setTimeout(properties.getCommandTimeout());
    }
    
    public void set(String key, String value) {
        connection.sync().set(key, value);
    }

How to achieve the linear performance increase with Redis cluster using the lettuce java client??