Default underline position misinterprets font’s specification
InDesign interprets the underline position as the center of the line (from which the "thickness" extends outward), whereas the OpenType spec calls for it to be the top of the line (from which the thickness extends downward). This causes inconsistencies with other application’s interpretation of the same font’s metadata.
This is the suggested distance of the top of the underline from the baseline (negative values indicate below baseline).
The PostScript definition of this FontInfo dictionary key (the y coordinate of the center of the stroke) is not used for historical reasons. The value of the PostScript key may be calculated by subtracting half the underlineThickness from the value of this field.