I'm no expert, but this doesn't jive with my experience.Anything over about .5 CC indicates you need more sanitizer and that you are getting into an area where you want to stay out of the spa
.5 cc would be considered an unusually low reading. 2-3.5 cc is more typical, with readings as high as 6 cc not unheard of.
"Shocking" as described in the context of my spa, doesn't really make sense either. I "shock" every time I add chlorine basically. I add as much as I think I can get away with without damaging equipment. 20ppm fc is about the target, give or take 5pp, depending on the initial test results.
Cya levels are a bit of a mystery, cause I haven't tested very often. I can say for sure that they've been between 50 and 20 since Halloween.
For us, at least, just keeping FC at all, at all times, is the goal. This is irrespective of CC readings.
CC readings come down after not using the tub for a few days, or by running the air jets.
Running the air jets causes PH to climb, although that is easy to deal with.
It's not clear to me why I should care what the CC is. Keeping up with FC, PH, and CYA, is enough for me to deal with.