OK,
I never thought you could dilute the CYA solution but it makes sense.

It's a best-guess table, so I always view the range of FC as connected to the range of CYA. If you have a CYA of 140, I would not let my FC be 8. It's PROBABLY Ok, but if you are having troubles at 8 then you should be at 11ppm or greater.

You can still dump and refill to get your CYA lower--140 is high, but you can use the high CYA methods safely.