4 ppm per day is on the high side of normal. Many people on this forum report such losses. I have as much confidence as anyone can possibly have based the wisdom of this forum and my test results that my pool is quite healthy, yet I lose about 4 ppm of FC. My pool is fully exposed to the sun all day and naturally heats to the low 90s at times.
Higher CYA does not increase chlorine demand. It does adjust the target number upward, but that is a one-time addition. It actually reduces chlorine demand. For example, if you are at 30 CYA with a target of 3-6 FC, and lose three ppm per day, in a week you will have added 21 ppm. If you jump to 50 CYA and a target of 6-8, it's a one-time addition of 3 ppm, but if the daily UV loss drops to 2.5, you're 0.5 ppm ahead after only seven days. Make sense?
In my very limited experience, there are diminishing returns on chlorine protection and CYA. The difference of jumping from 30 to 40 in my pool was pretty noticeable, probably close to 1 ppm per day. The effects of jumping from 40 to 50 were far less obvious. As usual, it is a trial and error process.