[exim] Controlling SA-exim logging

I use exim4 and spamassassin (sa-exim) on Debian 10.

About a dozen Google searches have failed to locate information on how to control the logging level of Spamassassin in that configuration. Maybe I'm having a bad search-fu day, but can anyone here point me to appropriate documentation?

Why:

I get six lines from spamd in mail.log for each message processed. Only two are interesting to me, the line identifying the message, and the line with the result. The prefork, connection, and setuid lines would be interesting if those steps failed, but not in the success case when things are working. The clean message / identified spam line does not contain any information I need that is not in the 'result': line.

I have been asked to hold logs for 180 days, so halving the size of a log file without halving its usefulness is helpful to me right now.

Ken