I found this calculator, its made to use mainly with cleanflight as entering the values is a cut and paste operation. Im not sure how to get the numbers right for librepilot but mabey its something that could be usefull for people especially for unsymetrical frames like the diatone et200 etc
iforce2d (guy who developed the calculator) also has a Youtube account with a video on it Worth checking out. People seem to have very good results after using the custom mixing values from it.
https://www.iforce2d.net/mixercalc/