You're over thinking this thing
Co2 does 2 things for us:
1. It carbs the beer to where we want it due to co2 per volume according to the stored temp. This is where the regulator is set. Set it and leave it.
2. Co2 pushes the beer from the keg to the spout. The ending pressure is affected by the resistance in the delivery system. This is variable. I'm sure there there are formulas to calculate all the coefficients and resistance and stuff for the lines, connectors and taps down to several decimal points and the length of the line can be calculated to the millimeter.
None of this matters if you are not getting a good pour. Use the programs to get you in the ball park and add a foot or two of line, its cheap. Like already mentioned it is much easier to cut some off than add.
If the pour is dribbling out, cut off 6 inches and try again. If foam is blasting all over the place then replace with a new line that is longer than you think you need.
All the science in the world doesn't matter if you are not getting the results you want. It really is that simple