Elasticsearch is using more memories

Question

I'm using Magento 2 eCommerce and we are having 400 sites(multi-website). Each website created a separate index. So overall I have 400 indices in elasticsearch and each has a store.size of 10kb-500kb.

curl --silent -X GET http://localhost:9200/_cat/indices?v

Sample results:

health status index                         uuid                   pri rep docs.count docs.deleted store.size pri.store.size
yellow open   magento2_product_271_v50 5gjgjagzR4SMne6UanBsXQ   1   1          1            3     19.3kb         19.3kb
yellow open   magento2_product_263_v50 Rkkh6UggS96ZIMDaoO7utQ   1   1          1            3     19.4kb         19.4kb

Overall indices data sizes are less than 500MB.

Elasticsearch node memory details:

1. RAM: 128GB
2. JVM HEAP: 50GB (We knew good practice is it should be within 32GB). But if we set JVM HEAP as 32GB, we got a circuit breaker exception(data too large).
3. Number of core: 48
4. Elasticsearch version: 7.13

Also, we observed elasticsearch node CPU usage(4%) and load average(2-3) are normal. The only problem is elasticsearch using high memory(60GB).

Here I have two questions

1. Overall indices size is less than 500MB, how elasticsearch is using more memory(60GB)? It is showing more memory usage even the site is in maintenance mode(which means no traffic).

2. How to optimize the elasticsearch memory to stop the circuit breaker exception? because we are planning to create another 600 indices

Any help would be much appreciated. Thanks in advance.