Doesn't work so well but can be useful if you want to check a test case. Compute R from the alpha which appears in the Alpha plot. Compute Alpha from the R which appears in the Reflection Coefficient plot via layer stripping. How big a discreet layerstripping step to take. Don't take it too small without using enough DFT points or you will get spurious oscillations.
More points is better but slower.
For refletion coefficients which get pretty close to one over a broad band, you may need to use more DFT points. You may find that adjusting it before loading a reflection coefficient gives a better looking interpolation for r and hence a better reconstruction of alpha. You must use the letter w for the frequency. Hit return while in this box to make the change in R effective and replot. Enter a formula for Alpha.