Thread pool configuration

Thanks for replying .

cluster configuration
Master -3 node (4 cpu, 20 gb ram)
coordinating -3 node (16 cpu, 98 GB,)
data- 5 node (28 cpu, 48 RAM)

And thread pool configuration is following
thread_pool:

search:

size: 64

queue_size: 500

min_queue_size: 10
max_queue_size: 1000
auto_queue_frame_size: 2000
target_response_time: 1s
http.enabled: true

Here we are getting rejection on search type of queries .

How should i scale the cluster or can i optimize thread pool configuration .

Regards,
Abhishek