For turbos with internal actuators use a gain less than 15, external wastegate use a ggain greater than 15. The ratio is used in manual mode to set the boost so the higher you go the more boost you run. Boost limit will cut off boost when it reaches the set value, I'm guessing that you've set the boost limit to 1.25 bar?
I don't have a GTR but do have a GTST with gain set to 12, ratio set to 54 (which works out to approx. 12psi of boost for my car) and limit set to 13psi. GTR owners will be able to tell u the safe boost level to run.