When a carpet track is green or the layout has just been changed, I will generally look for a little more rear grip so the car will be more consistent and easier to drive until grip comes up. As grip gets better and the track becomes more consistent, I undo those things to make the car rotate again. Usually I will adjust flex with the topdeck setting, or by using split arm mounts instead of solid, etc. You can also sauce differently, longer for more traction but less when grip is high.
I pretty much always run a 2k rear diff on carpet in 17.5 but my friends often adjust their rear diff to the track, starting at around 3k when grip is low and sometimes going as high as 10k when traction is good. I've tried doing that too, but I personally like how the 2k feels on corner entry no matter what the grip is like.
Hope this helps
