I use various base timings depending on the power of the car. This is ***ONLY*** done with the gtir's as they have a distributor, which are inherently unreliable on high power cars, and I find other settings more reliable at high power. This cannot just be adjusted too if the whole map has not been compensated (to be honest I still don't like to do this but sometimes it seems the only option, and for me it does work.
Unless your car has been tuned by me and I have told you otherwise, assume its running stock timing at 20 deg, and set it to that.