Re-read what the slap.conf(5) man page says.
That's unhelpful. It's of course, already been read.
man slapd.conf ... minssf=<factor> property specifies the minimum acceptable security strength factor ... maxssf=<factor> property specifies the maximum acceptable security strength factor ...
Reads to me like "SASL SSF" is set by min/maxssf. It certainly affects it. Unfortuntely, in a manner that's confusing.
If have some helpful clarification, please state it.
Thanks.