I'm trying to reduce space by reducing splunkd_access.log .4 & .5 as well as web_service.log .4 & .5 .
Doc is clear on metrics.log and I find that item in log.cfg . However this is not an exact match for web_service.log .
I did find an entry
appender.accesslog.maxFileSize=25000000 # default: 25MB (specified in bytes).
you found the place to change it. You can put log.cfg settings into a local file, log-local.cfg file, residing in the same directory as log.cfg. The settings in log-local.cfg take precedence. And unlike log.cfg, the log-local.cfg file doesn't get overwritten on upgrade.