NAs will be happy at 14.7:1 across the whole band.
For best torque and power it you would want the fuel around 13.2:1 - 12.7:1 depending on timing and exhaust flow, egt not a issue and det can be be kept under control with the advance maps.
I have never tuned a Siemens simos 3 so dont know the ecu mapping, but having timing pull of -3cf is fine, you need to remember the CF is actual pulled routine timing not actual pinking or det, you could have -12cf and still have no audiable det via the detcan. The ecu is only picking up voltage from the sensors, the ecu is trying to keep the voltage in check.
If your getting -3CF then you know your at least getting minimum best timing and making optimised power rather than running 0CF and not knowing if your getting thr best power.