With any setup parameter there is a sweet spot - any change in any direction away will give a decrease of what it has optimized..... and changing something else may unoptimize what was optimized elsewhere.
Therefore, very much trial and error... every track is different, every 5minute run is different on same track! due to temperature, weather, track wear etc etc etc...
But in a nutshell, have a good general setup starting point & listen to Rich Lowe..
