1.25 scale ratio was not chosen because it is 1.5/2.
I picked 1.25 scale ratio, because that was the only scale which also had 20px on it. Other scale ratios did not bring up scales with 20px value in them.
Having 20px on the chosen scale was critical for me, because 20px is my (base) body text line-height. A scale is harmonious only if it also has your (base) body line-height on it — since finally, you are trying to make everything harmonious to your (base) body text.
Hope this clarifies.