Hmm, ok, I would have thought that the spacing between lines was determined by the font height set in the .font file, but I might be wrong. @Mathias_Westerdahl will be able to tell us how it actually works tomorrow.
The line height is usually calculated from the maxAscent and maxDescent, which are in turn calculated when loading a font with a certain size. However, there are a many font tools out there, and there’s also some artistry required to fill in all info in a font. When loading this font in FontBook (Mac OS), it complains about the “hhea” table, which is responsible for the horizontal metrics.