Since TP is a theoretical number that changes greatly with a different MAF. If I'm creating a tune form scratch I will setup a decent range of TP load. Like low load of 10 and high load of 150. Then take it for a quick spin, and see where you are load wise while cruising, find what TP my 0psi is at, and make sure to not run too much time, and run rich at that TP and higher. Then I will do a WOT run and see how far my max TP goes. If it goes above 150, then I rescale the load to 200. Keep on doing this until you get a pretty consistent map that is linear.
Keep in mind it's not a good idea to run off the map, make sure your highest TP column is a good bit higher then your maximum actual TP.
NEMU RT is no different then regular Nissan ECU tuning (TP scale wise). NEMU SA with MAF is very similar too. This means this advice will work for all of the above.