This idea of tuning "one end" of a chassis' flex always perplexes me.

The end of a chassis you are tuning is only flexing relative to the tyres on the ground at the opposite end of the car (the middle of the car is not attached to anything), so it's basically impossible to isolate the actual flex from one end of the car to the other.

I can see how you might get some additional effects if, say, the front end of the chassis is flexing relative to the steering mechanism; but fundamentally, a flexy chassis will generate more grip and be less responsive, and a stiffer one will generate less grip and be more responsive.

I'm of the opinion that if your car stops getting quicker as the grip level increases at a track, then the chassis is too soft. I used to run a TOP Photon, and the standard 6-cell chassis was awesome on the first run of the day (rubber carpet). By the fourth run of the day it was grip rolling. Going one grade stiffer on the top deck made the car slower in round one, but better in the finals, which is where it counts.