Did you try the custom string feature? This is your best bet.
RacquetTune works on the frequency it hears to determine the tension and stiffness. The frequency of the string is proportion to the structure, length, and diameter of the string. When using a constant pull machine you are constantly pulling the string at a preset tension. The longer a string is pulled the smaller diameter the string will be because it is constantly stretching. As the string relaxes the tensioner continues to pull the strings to maintain a constant tension. Depending on whether you are pulling the mains or crosses there can be a larger difference.
When pulling the crosses there is friction between the string and the two points where it contacts the frame (same as mains) and all the intersecting points when the cross strings intersects or crosses a main (unlike the mains.) Each of these friction points tends to lower tension. So it stands to reason if I measure the tension on a string directly out of the tensioner it will be greater than the tension on the other side of the racket. I have a video that show that. if you allow the tension on crosses to pull longer you will have much more stretch than a main will have relevant to the string length. That's why the JET Technique pulls the crosses for a longer period of time than the mains, to give time for friction to be overcome.
All of this plus drawback, knots, and other differences has an effect on frequency. For all those reasons the RacquetTune app will never be 100% accurate. So what you should understand is what it is good for. You measure a racket off the machine and at various points after it comes off for a comparison. Also if you string for others what good does it do them is they don't know you 'custom' string setup. So they may get something totally different from what you get. So if they want 55 on RacquetTune and you reading is 57 who is to say who is rit?
I have the ability to drive people crazy, not sure if I was born with it or I learned it but I'm damn good at it.