I have 4 indexers and 3 search heads and I currently have a */local/limits.conf file as below for my SH settings:
[show_source]
max_count = 50000
distributed_search_limit = 50000
[search]
# the maximum number of concurrent searches per CPU
max_searches_per_cpu = 3
# the base number of concurrent searches
base_max_searches = 10
this answers is from a few years ago, but it might help.