It is probably best to just start with the stock O2 switch points and see how it goes. We just mentioned a flat-line of 450-550 mv as a switch point as many of us have had better results with that method.
But, for starters (IMO) it is easier and more consistent on your first few tunes to use your stock O2 switch points. You can aways apply the 'flatline' method as you narrow down your STFT's & LTFT's. At some point you can try just disabling your LTFT"S as Frost suggested and just run with STFT's. You can then manipulate your O2 switch points and other parameters to fine-tune it if necessary.