For me its simple ... follow the manufacturer's base settings. Then tune the high to its max and back off about 300-400 RPM. Then get your low end right, make sure it idles well and the transition is crisp. Then fly her and see ... of course when you fly you should pull verticals and listen to the engine, is it bogging down or its just happy and maintains the RPM. When you land check the engine temp to ensure you are not too lean.

Like the Rossi 45 I had, its a b*tch of an engine to tune, the high end has a narrow window for tuning and it needs to be flown to get it right. Your ST is not too fussy on the low end or high but if its like the G90 then you will be struggling with the mid range. I hated mine dspite being a cheap engine that is easy to start and its reliable. Oh yeah ... my G90 was not happy with more than 5% nitro.