Tweaking MergePolicyConfig for usecases with lots of updates/deletes

We'd like to know how to go about tweaking MergePolicyConfig for ES7
https://www.javadoc.io/static/org.elasticsearch/elasticsearch/6.7.2/org/elasticsearch/index/MergePolicyConfig.html

We've been noticing many segments reaching the 5gb limit. We are also seeing too many deleted documents that have not been reclaimed from the system