The sliders in the config take precedence over the tray controls on restart/startup, and are not "live" - any changes made in the config requires a restart. The tray sliders are "live", and will make adjustments w/o having to restart. BTW, it's the right click that opens the brightness/contrast, left clicking will eventually open the config panel, or at least that's how it works on mine.
75/35 here, seems to give the best display view for me, then again, I am about blind, and my system sits nearly on the floor, and to my left somewhat.
Belgarius