Wheel size makes very little difference in small increments, it's mainly done off weight. 1" will use practically the same settings. Hence the front needs higher pressure, as that is where there is most weight (the engine). I tend to run the same front and rear because a) I like the rear tyres to feel firm (this is not always best for grip) and b) I run a 24kg sub, 2 amps and a MDF stealth shelf with 6x9's in (old school, I know), which adds more weight in the back.