There is a great way to have more accurate scores !
You can partecipate in spamassassin community (https://ruleqa.spamassassin.org/) to have scores that consider also your samples and are more accurate also for you when you update official spamassassin channel.
I wrote a little instructions to do this within an EFA box
It is very very simple and takes about 30min daily for 15k mails
Read file contained into attached zip
Questions and answers about how to do stuff
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