I threw out the official CoC rules for Sanity well over a decade ago (I also run games under d20 3.5 rules, not BRP).
My replacement system is called “Monster Familiarity”.
If you not only survive but triumph against a specific type of monster, say Deep Ones, then you get a +2 bonus to SAN checks every time you face them in the future, up to a maximum of +20. So triumph against Deep Ones ten times, and you’re not likely to go mad from facing them at any point in the future. They might EAT you, but at least they won’t drive you to insanity.
Record this on your character sheet as “Monster Familiarity (Deep Ones): +2”
For every creature you “max out” at a +20 bonus, you receive a +1 bonus to ALL future SAN checks; this doesn’t stack with the bonuses for specific creatures. So once you’re “quite familiar” with Deep Ones, if you then encounter some Ghouls, you’re starting out with a +1 bonus to not freak out upon seeing them. And if you triumph enough against Ghouls to “max out” your Monster Familiarity bonus for them as well, your general SAN check bonus goes up to +2; this is also up to a maximum of +20.
Record this on your character sheet as “Sanity Check Bonus (All): +1”
Anyhow, that’s why, even though I own the 7th Edition books, I’ve never even looked at the Sanity section, as I don’t really care what’s in it.